JMC : Logic and Mental Philosophy / by Charles Coppens, S.J.

Chapter III.
Means of Attaining Certainty.

100. The means at our disposal to attain certainty are directly, our own cognoscive powers or faculties, viz., intellect and sensation, and, indirectly, the authority of other men. To explain these clearly we must treat: 1. Of our cognoscive Powers in general; 2. Of Intellect in particular; 3. Of sensation; 4. Of authority. To all this we shall add a chapter on common sense, which, though proceeding from the intellect, requires for the discussion of its certainty the previous understanding of the reliability of intellect, sensation, and authority.


101. I. The outer senses. Our first step in the acquisition of knowledge is the perception of material objects by means of material instruments which are parts of ourselves, and are called the organs of sense.

102. An organ is a part of a living body peculiarly constructed by the Creator for the purpose of exercising a function of life. Living bodies are made up of such organs. In man, and in the higher animals generally, five of these organs are intended for the perception of exterior bodily objects; these are called the organs of the five outer or exterior senses, viz., of the sight, hearing, smell, taste, and touch.{1}

103. II. The inner sense. There is, besides, an internal or inner sense, whose organ is some portion at least of the nervous system; it perceives interior modifications of the animal such as cause the feelings of hunger, thirst, fatigue, pain, comfort, etc. It also perceives the actions and affections of the various external senses; for an animal not only sees, hears, tastes, etc., but it also feels that it sees, hears, tastes, etc. This inner sense, in as far as it takes cognizance of what is done by the outer senses, is often called the common sense, and its organ is styled the common sensory; but the term common sense without the definite article 'the,' stands for a very difierent idea, viz., for the common judgment of men on matters of universal importance to mankind.

104. The inner sense does not perceive the causes of the affections which it perceives, but only the fact that those affections exist. As both the objects of sensation and its organs are material, the action of all sensation is material, organic, and is common to man and brute. But the organ is, of course, not dead but living matter; it is one substance with the soul, i.e., with the principle of life; hence the actions of any sense are actions of the living compound soul and body.

105. III. The imagination. When an animal perceives material objects, it forms and retains of them material images or representations, called phantasms. The organ used for these purposes is the brain. The imagination is the power of forming and retaining those images, of recalling them on occasions, and of combining them in wonderful varieties, thus forming new phantasms which in turn may be recorded and retained, etc. We should not suppose those images to be pictures, for we can have no picture of taste, smell, etc.; they are modifications of some kind.

106. IV. The sensile memory. This name denotes that portion of the imaginative power which retains and recalls the phantasms, but it adds a further function, viz., that of recognizing, not intellectually however, present sense-perceptions and present phantasms as identical with former phantasms and former sense-perceptions. By this faculty "The ox knoweth his owner, and the ass his master's crib," as Holy Writ expresses it. The inner sense, the common sense, the imagination, and the sensile memory need not be considered as distinct faculties, but rather as various functions of the same faculty, which may be generally designated as the inner sense.

107. V. The intellect, understanding, or mind, in the proper meaning of this term, is an entirely different faculty; it does not confine its perceptions to the material qualities of objects, as all sense-action does, but it penetrates into the very essences of things material and immaterial (intus legit, it reads within), and it forms concepts or ideas representing essences, e.g., of 'plant,' 'tree,' 'spirit,' etc. Even when it considers mere accidents, e.g., 'color,' 'shape,' 'size,' it need not simply consider this individual color, shape, or size, as material faculties must do, but it can consider the essence of color, shape, and size; so that, by a power peculiar to itself it forms ideas representing qualities as abstract -- i.e., drawn forth, as it were, from the subjects in which they are found and thus stripped of their individuality.

108. VI. The judgment. Besides conceiving ideas, the intellect judges; i.e., it compares two ideas together and pronounces on their agreement or disagreement. This act of the intellect is called judgment; it was explained in Dialectics I. 17).

109. VII. Reason is not a faculty distinct from the intellect and the judgtnent; it is the intellectual act or process of deriving judgments from other judgments; it, too, was sufficiently explained above (No. 22).

110. VIII. The intellectual memory is another function of the intellect; it enables us to perceive and reproduce ideas, judgments, and reasonings formerly elicited, and to recognize identity or difference between present and former objects of knowledge. The intellectual memory is greatly assisted in its action by the sensile memory, which associates phantasms with mental concepts.

111. IX. Consciousness is the intellectual power of perceiving our own internal acts, whether of intellect and will or of our interior sense; it will be more fully explained in the following article.


112. The intellect or understanding may be called the universal means by which certainty is to be acquired; for certainty is a state of the mind or intellect, and therefore it cannot be reached except by the intellect. That the intellect may begin to act, it must be excited by sensation; and therefore those whose senses are very imperfect remain idiotic. But sense, no matter how perfect, can never elicit a judgment. Still, sense is a means by which the human intellect is brought into communication with many objects of knowledge, and the reliability of sense-perception will be examined in the next article.

113. We are just now concerned with the certainty of intellectual knowledge as such. We must begin this study by recalling to mind that the first condition for the attaining of all certainty is the capacity of the intellect to reach truth. We need not, then, prove the reliability of our intellect. But we must here examine what is involved or included in this capacity of the intellect to know truth.

It involves the certainty, 1. Of consciousness; 2. Of our primary ideas; 3. Of immediate analytical judgments; 4. Of the intellectual memory; 5. Of the reasoning process. We shall examine the reliability of these functions of the intellect in detail; in doing so, we shall scientifically explain rather than prove our theses; for the first condition of certainty needs no proof.

§ 1. Consciousness.

114. Consciousness is the reflex perception of our own acts, i.e., of ourselves as acting. We not oniy think and feel, but, when we reflect, our mind perceives that we think and feel. This reflection consists, as the word indicates (reflectere, to bend back), in the bending back of the mind upon itself, upon its own acts. Reflection is, of course, not the beginning of our knowledge; for we must first think and feel before we can perceive that we think and feel. But when we scrutinize our own knowledge, this reflection on self is the first act to be examined in the process of our study.

115. This reflection should not be confounded with reflection in the sense of remembrance. Nor should consciousness be mistaken for the inner sense, explained above (No. 103). It differs from it: (a) In the subject that elicits the act; consciousness is elicited by the simple intellect, sensation by the human compound; (b) In the object perceived: consciousness perceives both simple and organic actions, the inner sense organic actions only; (c) In the manner of perception; the perception of sense terminates in phantasms, thet of consciousness in ideas and judgments, affirming that the facts exist, i.e., that we really think or feel as we are conscious we do. But consciousness is not the function which perceives what are the causes of our feelings, e.g., the causes of pain or comfort experienced; such causes are made known to us by reasoning and repeated observation united, i.e., by induction.

116. Thesis V. The reliability of consciousness is included in our capacity to know truth.

Explanation. We are not proving our capacity to know truth; this capacity needs no proof (Nos. 97, 98); but we maintain here that this same capacity of our intellect to know truth could not exist unless our consciousness were reliable.

Proof. That is included in our capacity to know truth, without which we could never know whether we know or not, but without the reliability of consciousness we could never know whether we know or not. Therefore --

We prove the minor. It is only through consciousness that we know our own intellectual acts; therefore, if consciousness were not reliable, we could not really know whether we are eliciting acts of knowledge.

117. It will be noticed that the field of consciousness covers the following objects of knowledge: 1. Our own existence; for we perceive ourselves as being the subjects of our intellectual acts and of our sensations. 2. The existence of our intellectuaI acts. 3. The existence of our internal sense and of its acts.

118. It may be objected: 1. We are not conscious of all our internal acts. We answer. We claim certainty for those only of which we are conscious.

2. Many persons are conscious of affections which do not exist; e. g, that they are ill when they are not ill. We answer: They are conscious of certain feelings, from which they infer by faulty reasoning that they are ill. Consciousness reveals only the existence of the feelings, not their causes.

3. Lunatics are conscious of being kings, princes, etc. Answer. They are conscious of judging themselves to be kings, etc., and they do judge so owing to their diseased imagination. For lunacy supposes an inability to distinguish between imaginations and real perceptions; but the consciousness of even a lunatic is reliable.

4. No one can know that his certainty is not owing to a diseased imagination. Answer. If so, universal Scepticism would follow, and the intellect would be incapable of knowing truth.

5. The proof takes for granted the reliability of our consciousness, the point to be proved. Answer. We are not giving a strict proof, but only a scientific explanation; for the first truths cannot be strictly proved and need no demonstration.

§ 2. Primary Ideas.

119. By primary ideas we do not mean inborn ideas; for no ideas are inborn in us: we have no ideas antecedently to sense-perception. But whereas by sense we form phantasms or matenal images of bodies observed, we form by our intellect ideas or immaterial images of what is cognoscible in those bodies; e.g., of 'being,' 'substance,' 'size,' 'color,' etc. The objects of sense are necessarily individual, extrinsic, and concrete qualities; the proper objects of the intellectual idea are universal and abstract notes.

120. We call primary ideas those of 'being,' 'truth,' 'substance,'' cause,' 'effect,' etc.; all those, namely, that are involved in our commonest perceptions. Of these we assert that they have objective truth, and that their objective truth is implied in the very capacity of our intellect to understand truth. Kant makes them subjective forms only, to which nothing objective corresponds.

121. Thesis VI. Our primary ideas are objectively true, i.e., conformable to objects really existing.

Proof. If these ideas were not objectively true, not conformable to objects really existing, our commonest knowledge would be but an illusion; if, for instance, 'being,' 'truth,' 'substance,' etc., were mere figments of the imagination or of the intellect, we could never know anything. Therefore they are objectively true.

122. It must be carefully noticed, however, that the object of a universal idea does not really exist as a universal object: everything that really exists is an individual thing. Likewise, the object of an abstract idea does not really exist as an abstract object: every existing being is concrete. For instance, there exists no real abstract or universal cause, nor any real abstract and universal effect, substance, being, etc., just as there exists no real abstract or universal animal, which would be neither rational nor irrational, but simply have the qualities that make up the genus animal. How, then, is the idea 'animal' objectively true? Because the qualities expressed by the term 'animal' really exist in every individual animal. Nothing, then, in nature exists in the abstract; but anything may be viewed in the abstract by the intellect, and abstract notes are the distinctive objects of intellectual cognition.

123. Now, the abstract idea is the same as the universal idea: the word 'abstract' denotes the manner in which such an idea is formed, while the word universal denotes its applicability to many objects. Thus, I form the abstract idea 'animal' by attending to the notes, which I perceive in any individual animal, viz., 'a material substance endowed with life and feeling'; these notes I draw forth, or abstract (abstraho), for separate consideration, or, if you wish, I withdraw my attention from the other qualities of that same individual animal which I am considering. Since these same notes conceived are common to all animals, my concept of 'animal, is a universal concept, i.e., it is predicable of a whole class. In as far as my idea 'animal' denotes only the qualities or notes that make up its comprehension, it is called a direct universal; but when I reflect besides that the idea is applicable to many beings, i.e., when I consider also its extension, the idea is then called a reflex universal.

124. Philosophers have warmly disputed upon the nature of these reflex universals: the Nominalists call them mere names, which are given to a confused collection of individuals, but to which no concepts correspond; the Conceptualists call them concepts, but they suppose those concepts to be mere figments of the intellect to which no real objects correspond; the Exaggerated Realists supposed that universal beings really exist corresponding to the universal concepts; the Moderate Realists maintain that some reality in objects corresponds to the abstract idea, yet that such reality does not exist objectively as an abstract or universal being without individualizing notes, but it exists concretely in each individual object. The explanation we have given in the two preceding numbers is that of the moderate realists; but the scientific proofs of our doctrine and the refutation of other systems belong to Psychology.

§ 3. Immediate Analytical Judgments.

125. Analytical judgments, as explained above (No. 17), are those judgments in which the agreement or disagreement of the subject and predicate is perceived by the mere analysis of their meaning, without the aid of experience. If this agreement or disagreement is perceived at once, without reasoning, the judgments are said to be immediate.

126. Thesis VII. Immediate analytical judgments can never be false.

Proof 1. That such judgments cannot be false is made evident by considering their very nature; for they consist in affirming or denying explicitly what the very idea of the subject contained or excluded implicitly; e.g., when I conceive 'a part,' I conceive something as distinct from 'the whole,' and distinct from it by being less. Thus all immediate analytical judgments, e.g., 'The part is less than the whole,' do no more than affirm or deny explicitly what the subject of them contained or excluded implicitly before the judgment was formed.

Proof 2. Our intellect has the power to know truth (No. 98). Therefore that can give us real certainty which is implied in the capacity of our intellect to know truth, or which must be objectively true if the intellect can know truth at all. But such are these judgments. For if our intellect could not be relied on in these judgments, e.g., that 'a circle is round,' that 'a part is less than the whole,' etc., then the intellect could never be relied on in any judgments; for none are more evident. Therefore it can be relied on in these: they give us real certainty.

127. Objections: 1. This thesis cannot be demonstrated. Answer. It need not be; for it is evident.

2. Some of the judgments are false, e.g., "The whole is greater than the part"; for the whole Blessed Trinity is not greater than any of the Persons. Answer. The Divine Persons are not parts of God; each of them is the infinite God whole and entire.

3. Another of these judgments is false, viz., "Out of nothing nothing can be made"; for the world was made out of nothing. Answer. This analytical judgment means that nothingness cannot be a material out of which a thing can be made, while, in creating, God made the world without using any material; He did not make nothingness the material of His creation.

4. All our judgments are empirical; for they presuppose sensation. Answer. They presuppose sensation before we can conceive the ideas, we grant; they compare the ideas by attending to experience and sensation, we deny. Now, the latter is required for empiric judgments. (No. 17.)

5. No judgments are certain; for to err is natural to man. Answer. To err sometimes in his opinions, yes; to err in his certain judgments, no.

6. Analytical judgments are useless; for their predicates are contained in their subjects, even though no judgments be elicited. Answer. They formally and explicitly discover and express what predicates are implicitly contained in their subjects.

§ 4. Memory.

128. Memory is the power of retaining and re-awaking former knowledge, and of recognizing it as former knowledge. It is twofold:

1. The sensile memory retains and re-awakes phantasms -- e.g., of a whip formerly seen or heard and of a pain felt -- and it perceives a connection or association between those phantasms. In this way brutes remember as well as men. (No. 106.)

2. The intellectual memory retains and re-awakes ideas -- e.g., of what we formerly saw, felt, read, thought, or willed -- and it judges that the objects of those ideas were formerly perceived. In man the sensile and the intellectual memory work together and assist each other.

129. The memory acts voluntarily when it recalls the past at will; spontaneously, when the will has no share in act. To act spontaneously, the memory must be aroused by a perception in some way associated with a former perception e.g., the fragrance of a fruit may recall its taste; the idea of eternity may recall the shortness of this present life.

130. Thesis VIII. The reliability of our memory is contained in our power to know truth.

Explanation. We do not maintain that we can recall all our former perceptions; but simply that, when our memory does recall a former perception, and judges with certainty that the object now recalled is identical with an object perceived before, it is reliable in such a judgment, and that this reliability of the memory is contained in the power of our intellect to know truth.

Proof. That is included in the intellect's power to know truth, without which all connected thought and all expression of thought would be impossible. But the reliability of our memory is such. For, unless our memory were reliable, we could not think connectedly, since one judgment would be forgotten before another could be compared with it; and no thought could be expressed, because no words could be remembered to express them.

131. If it be objected that our memory often deceives us, we answer: Not when it gives us, on careful consideration, positive testimony, excluding all fear of error. But men are often too careless, impatient, or presumptuous to examine their recollections properly.

§ 5. Reasoning.

132. When we attempt to reason in order to prove the reliability of reasoning, we evidently do not pretend to give a strict proof; we simply give a scientific explanation, showing why it is that a conclusion logically derived from true premises must be as certain as the premises themselves.

133. Thesis IX. Whoever grants the premises of logical reasoning cannot deny the conclusion.

Proof. All logical reasoning, as explained above (Nos. 22, etc.), is based on this principle, that the conclusion is implicitly contained in the premises. Hence, he who would grant the premises and deny the conclusion would thereby affirm and deny the same thing; but one cannot deny what he affirms. Therefore whoever grants the premises of logical reasoning cannot deny the conclusion.

134. Objections: 1. If the conclusion were contained in the premises, nothing new would be learned by reasoning. Answer. The knowledge of the conclusion is new to us; for, although the conclusion was implicitly contained in the premises, we did not know this conclusion in particular till we arrived at it by reasoning. Thus, all the theorems of Geometry are derived from the preceding theorems and ultimately from the axioms.

2. Reasoning leads men into many errors. Answer. Not when it is materially and formally correct.

3. The proof given holds only for the syllogism. Answer. All reasoning is reducible to the syllogistic. (See Nos. 35, etc.; in particular, for induction, No. 46.)


135. The faculty of sensation distinguishes all animals from all vegetable substances; for 'sentient' is the difference which, added to the genus 'living material substance,' constitutes the species 'animal.' By saying man is an 'animal' we mean exactly this, that he is a living material substance endowed with sense.

136. Now, sense is a cognitive power, i.e., a power of knowing; its action, or knowledge, is elicited by a living material substance, and its organs consist of the living material nerves. It is a clear and certain principle that no action can be superior to the agent, else the effect would exceed the cause; therefore, as sense is a material power, it can know nothing higher than material objects.

137. Besides, any matter is a concrete individual portion of matter; both the organs and the objects of sense are such, and therefore every sense-action will be a concrete individual modification of a concrete individual portion of matter. But it is evident that a concrete individual modification of a concrete individual portion of matter can picture or represent by its own nature nothing but a concrete and individual modification of matter; now, perception of sense consists in such representation, hence sense can perceive nothing but concrete and individual modifications of matter.

138. When sense perceives the material modifications that take place within its own animal body, it is called inner sense; when it perceives the material modifications that take place outside of its animal body, it is called outer sense. Inner sense was more fully explained above (Nos. 103, 104).

§ 1. The Inner Sense.

139. The inner sense does not testify to the causes of our feelings or affections; for by our inner sense we merely feel a certain affection called pain or comfort; by our animal instinct we are prompted to seek relief of the pain or increase of the comfort; but it is only by a process of inductive reasoning that we have learned intellectually to refer this certain feeling to a special cause. Thus we have learned by long experience that a peculiar feeling of discomfort arises from want of food, another from want of drink, etc.

140. Thesis X. Inner sense is reliable in its perceptions i.e., the material modifications perceived by it really exist.

Proof. To say that the inner sense is not reliable in its perceptions, is the same as to say that those identical affections, or inner modifications of the animal body, which are perceived, do not really exist. But this cannot be said without absurdity; for 'to be perceived' means 'to be that which is perceived' or 'to exist as the object of perception.' If, then, those affections did not really exist, they would 'exist and not exist'; which is absurd.

141. Objections: 1. The inner sense sometimes testifies to the feeling of a pain in an amputated limb. Answer. It testifies to the feeling of a pain, we grant, and there really is a pain; but it does not testify to the exact cause of that pain. The feeling experienced now may be similar to that experienced before the limb was amputated. Then the feeling of pain arose from some lesion in that limb; and now, the imagination reproducing this former relation, affords us an occasion for judging that the present sensation is again owing to the limb which is no longer there. We feel a lesion, which we may be inclined, by the force of habit, to locate in the amputated limb, whereas the nerves are affected elsewhere, namely at their extremity, which is exposed and very sensitive.

2. The inner sense fails to report all affections. Answer. We simply maintain that those affections exist which it does report.

3. The proof supposes that the inner affections are really felt and therefore must really exist; but perhaps we only imagine that we feel them. Answer. We know by consciousness that we can imagine a certain pain, for instance the pain of burning, and that we can feel that pain, but that there is a vast difference between these two acts.{2}

§ 2. The Outer Senses.

142. We stated before (No. 102) that we perceive objects outside of us by the five outer senses of sight, hearing, smell, taste, and touch. Two very different questions present themselves on this subject: 1. How far is the testimony of our external senses reliable? 2. How do the senses work so as to give us reliable testimony? The full treatment of the latter question belongs to Psychology, that of the former to our present study of Critical Logic. We are absolutely certain of many facts, though we cannot satisfactorily explain how they are brought about: a man exhausted with hunger and fatigue is absolutely certain of the pleasure and the restoration of strength which he derives from a wholesome meal, although he cannot explain the exact process by which the senses and the digestive power contribute to these results; similarly, all men are certain that the outer senses often give reliable information, though few are able to describe the manner in which this is accomplished.

143. The obvious facts in the case are these: (a) We have various sensations of outer objects in and by our external senses; (b) We judge the cause of these to exist in bodies, i.e., in substances distinct from our mind, having extension and peculiar powers of action; (c) We adhere to this judgment firmly without fear of error. We maintain that our firm adhesion to this judgment is due to the objective existence of bodies, and that therefore our external senses are reliable in their sensations of outward objects.

144. But some philosophers argue that we do not know bodies except by means of phantasms and ideas, which are subjective in us, and which, for all we know, may have no objective reality corresponding to them. These philosophers are called Idealists. They are divided into two schools: 1, Fichte, the leader of the subjective school, maintains that there exists nothing but his own mind which is ever imagining unrealities: "The Ego posits itself." 2. Berkeley, the leader of the objective school, makes God the direct cause of our phantasms and ideas.

145. Such speculations, instead of resting on solid facts, as all sciences should do, are in direct conflict with all known facts and with the firmest judgments of all mankind. Every sound mind knows for certain the difference between real perceptions and mere imaginations; and unsoundness of mind consists precisely in the inability of some men to distinguish between objective realities and mere phantasms. But there is no likelihood that any philosopher of note ever doubted the existence of bodies. Such as pretended to doubt did violence to their own good sense in order to support some pet theory, by which they earned the name of original thinkers.{3}

146. Thesis XI. By our external senses we really perceive bodies, i.e., substances distinct from our mind, extended and resisting.

Proof. Nothing exists without a reason for it; but there exist in us, as we know by consciousness, (a) Sensations; (b) Irresistible judgments that those sensations are caused by bodies, i.e., by substances distinct from our mind, extended and resisting; therefore a reason must exist for those sensations and for those irresistible judgments. But that reason can be none other than bodies really existing; therefore they really exist.

We prove the last minor: If that reason were not in the bodies, it would be either, 1. In our minds, as Fichte maintains; or, 2. In God, as Berkeley supposes. No other reason is assigned by our opponents. Now, it is, 1, Not in our minds. If it were, we should produce those sensations and judgments necessarily or freely; but we do neither: (a) Not freely, for we see, hear, feel, etc., many things which we are totally unwilling to see, hear, feel, etc.; (b) Not necessarily; for if we were so constituted that we necessarily elicited false judgments, our intellect would be essentially unreliable; it would be a power, not of knowing truth but of deception and falsification. 2. Not in God. Those who admit the existence of God at all, as Berkeley and his followers do, admit that He is the infinitely perfect Being; but a perfect being is essentially truthful and cannot be the source of a universal deception, as He would be if He produced those phantasms and gave us at the same time an irresistible impulse to judge falsely of their cause.

147. Objections: 1. An evil genius could produce the deception. Answer. We deny this; for the deception, if such it were, would be, not accidental, but natural and essential to man, and therefore it would be essential to man to judge falsely; and thus universal Scepticism would become reasonable.

2. God would not be omnipotent if he could not directly produce on us all the effects that bodies can. Answer. He cannot give us an irresistible propensity to judge falsely; this would be against His own perfect nature, and it would leave us incapable of having certainty, of knowing truth.

3. God does so in visions, e.g., when He made Tobias see an Angel. Answer. The Angel had assumed a material body.

4. Sometimes a vision is merely subjective. Answer. Then the intellect sees reason to suspect the truth.

5. In dreams we judge irresistibly that we perceive real objects. Answer. In dreams we do not examine the certainty of our judgments; we have not that reflex certainty which we are here considering. Besides, in dreams we are not in the normal state of rational beings.

6. Those suffering of mania a potu cannot rid themselves, even on reflection, of the perception, as they suppose it to be, of snakes, demons, etc. Answer. From the fact that a disordered mind cannot know the truth, it does not follow that a sound mind cannot; besides, they no doubt perceive their own abnormal condition and see reasons, when they reflect at all, to doubt their visions.

7. From any act which is only subjective we cannot infer the existence of the objective reality; but sensation is only subjective. Answer. Our sensation is not merely subjective; for it is a perception, and a perception is the subjective act of taking in an object: a perception without an object perceived is a self-contradiction: there can be no taking in of nothing. Besides, we invincibly judge that our perceptions are due to objects (Nos. 143, etc.)

148. To understand how far the reliability of our senses extends, we have only to examine on what points sensation prompts us irresistibly to elicit judgments. As this is a question of great importance, we shall consider it with some detail.{4}

1. We may see a painting in the distanoe and judge it to be a statue; we may judge a sound to come from a greater distance than it does. Do our senses deceive us on those occasions? Not at all: in fact, the sight, as such, does not inform us whether all the parts of the object seen are equally near, as in a painting, or unequally, as in a statue. Neither sight nor hearing, as such, tell about distances: sight deals with color and, consequently, with the outlines of colored objects; hearing deals with sound, of which we perceive countless varieties. Each sense has thus its own proper object of sense-perception (sensibile proprium). The proper object of sight is color; of hearing, sound; of smell, odor; of taste, flavor; of touch, temperature and resistance. The perception of resistance enables us to distinguish between varieties of surfaces, some of which are noticed to be yielding or soft, others unyielding or hard; some are even or smooth; some uneven or rough; some are bounded by straight, others by curved lines; some extend over a large, others over a small space, etc.

2. As extension, outline or figure, number, etc., are perceptible by touch and sight, they, and in general all those qualities of bodies which are perceptible by more than one sense, are called the common objects of sense-perception (sensibile commune).

3. Sense does not perceive color, sound, resistance, etc., in the abstract; but it perceives something colored, sounding, resisting, etc., in the concrete.

4. While by our senses we perceive some concrete body as colored, resisting, etc., our intellect, by its power of abstraction, abstracts, or considers apart, various notes or marks of that body, such as 'color,' 'resistance,' 'existence,' 'quality,' 'substance,' etc., and thus forms abstract ideas; next, by its power of judging, it compares these ideas and the objects perceived together, and pronounces judgments, such as 'this substance is colored,' 'something resisting exists,' etc.

5. The senses usually assist each other: the eye beholds what the hand touches; the ear perceives the sound, the eye the figure of the rattle or the string which fhe fingers move. Thus from earliest infancy we have learned by practice to associate our senseperceptions with one another and with our intellectual acts; we have perfected our associations of phantasms by inductive reasoning, till we have acquired great readiness to judge of the qualities revealed to one sense by the proper object of another sense. For instance, on hearing a familiar human voice we know the presence and the very expression of countenance of a well known person; from the fragrance of a fruit we can tell its taste; from the aroma we judge the form of a flower.

6. We see many reasons to judge, and on many points no reason to doubt, that the senses of brute animals work in the same way as our own. Brutes perceive the proper and the common objects of sense; and, as their organs and their instincts are often more perfect than ours, brutes may associate phantasms, derived from various senses, more readily and perfectly than we do, as is well exemplified in the scent of the dog and the cunning ways of the fox.

7. Sense does not perceive substance as such; i.e., as distinct from quality; but still, by perceiving the concrete qualities, it puts us into relation with substance. What is thus intellectually perceived on account of sense, is said to be indirectly sensible (sensibile per accidens). Brutes do not judge at all, in the proper sense of the word; they merely associate, e.g., the stone thrown with the man who throws it, and they do not always do even that: the dog will often bite the stone itself. The Creator, in His wisdom, has given brutes as perfect a power of associating phantasms as is beneficial to themselves and to man, for whose advantage they are evidently intended.

8. Man both associates and judges; for he has instinct and reason. It is, however, only on occasions of some importance that we stop to consider whether our judgments are well enough founded to exclude all doubt. We find them to be such when, on careful examination, we perceive that they give us evidence of the objective truth. That they may do so with regard to our sense perceptions, the following conditions must be fulfilled: (a) We must be conscious that we are in a normal or healthy condition; else we can see reason to suspect the testimony of our senses. (b) We must be aware that our surroundings appear normal; e.g., if all around us looked yellow, we should see reason to suspect that our eyes were jaundiced. (c) We must find that our senses are concordant with one another and constant in their testimony; e.g., if a passing glance makes me perceive an unusual appearance, I look again with care, I shift my position to dispel all possible illusion of the sight; or I even apply my hands to touch what excites my surprise.

149. Thesis XII. The external senses, acting under proper conditions, are reliable with regard to their proper and their common objects of sensation.

The proper conditions here spoken of have just been explained. This thesis defines the extent to which the outer senses are perfectly reliable.

Proof. The senses are reliable in their testimony if they perceive nothing but the objective truth; but such is the case. For, being physical powers, they work necessarily, and therefore they can only perceive the objects presented to them; else they would perceive what does not exist; i.e., that which does not exist would be an object of perception; which is absurd.

150. We do not, then, claim certainty for every judgment that is formed on occasion of sense-perception, but only for what the senses really report, i.e., the existence of those sensible qualities which are the proper and the common objects of sensation. The substance itself in which those sensible qualities exist is not apprehended, by the senses, as distinct from those qualities. From the knowledge of the qualities perceived by sense, the intellect judges the nature of the substance in which those qualities inhere. In forming its estimate of that substance, the intellect may often be mistaken; e.g., it may judge that to be an orange which is a lump of wax; it may mistake a picture for a body. But even in such cases the intellect is not led necessarily into error, but it can suspend its judgment till all fear of error has been removed.

151. Objections: 1. The senses tell us that sugar is sweet, fire hot, etc., while Descartes and others prove that these qualities are not in the bodies perceived, but in the senses. Answer. When we say that sugar is sweet, fire hot, etc., we mean that those bodies have real qualities which produce in us corresponding sensations of sweetness, heat, etc. ; both the qualities that are in those bodies and the sensations that are in us are denominated by the same terms analogically. Certainly sugar and fire have real qualities which are causes of our sensations.

2. We know by science that the sun is not exactly there where we see it; here the sight deceives us. Answer. We know by the sight nothing but the color of the sun; its place, size, etc., are inferred by inductive reasoning.

3. But even the color of the sun is not such as we see it when modified by the atmosphere. Answer. We do not claim certainty except for what we perceive; now, we perceive by the sight the color such as it is when it reaches our eyes; with anything else the sense of sight has nothing to do.

4. But the sight distorts its objects; thus, a square tower appears round in the distance. Answer. The sight reports only the colors of the different parts of the tower; all inference as to its shape, size, etc., are conclusions of inductive reasoning, which is often too imperfect to give certainty.

5. By admitting that the senses must be concordant and constant in their testimony, we imply that each sense singly can be mistaken in certain cases, at least for a while. Answer. All we imply is that the senses give no sufficient ground for certainty till we have examined whether all the conditions are complied with.

6. When I see a stick plunged into water, I see it broken where it touches the surface; here my sight deceives me. Answer. My sight reports the truth, viz.: that the stick appears as if broken.

7. Then our senses can report appearances only; e.g., that I see the appearance of a man, not that I see a man. Answer. Sense apprehends appearances only; but our intellect understands that appearances are accidents which naturally exist in substances. When I see the appearance of a man, I understand there must be a cause for that appearance; and, by attending to all the circumstances of the particular case, my mind soon forms a judgment, often absolutely certain, that on the present occasion the appearance of the man is due to the reality of his presence.

8. That our senses may be relied on, we must first know that the order of nature is constant; but we cannot learn this except from the testimony of the senses; therefore we cannot reason on this subject except in a vicious circle. Answer. We deny the major and the supposition that we need to reason at all in order to see the evidence of the common and the proper objects of sense, when the required conditions are attended to. We see color, we feel heat and resistance immediately.

9. A color, odor, taste, etc., may please one man and displease another; therefore different men must apprehend objects differently; therefore all do not apprehend them correctly. Answer. The apprehensions are the same, but they do not suit all alike. As the organs of men are substantially alike in structure, with only accidental differences, we reasonably judge that the apprehensions of all men by sense are substantially the same, with only accidental differences. But the pleasure arising from colors and sounds is mostly due to associations of phantasms and sentiments; thus, orange and green please persons of different parties. Odors and tastes, being intended by the Creator to guide us in the selection of suitable food according to our varying bodily conditions, though identical in kind, will often please one and displease another, according to our several needs, thus displaying the wonderful wisdom with which Providence adapts means to an end.

10. In the Holy Eucharist the senses are deceived. Answer. They apprehend the appearances which really exist, and thus there is no deception of the senses.

11. Persons who are color-blind misjudge colors. Answer. Rather, they are unable to distinguish colors sufficiently to judge with certainty.


152. Consciousness and intellect put us into direct communication with objective truth, of which they see the evidence. Their perceptions are called intuitions, i.e., visions of truth. It is the same with our sense-perceptions of the proper and the common objects of sense: they, too, give us intuitions or immediate evidence. Reasoning brings evidence to us in a more circuitous way; it gives mediate evidence. Such, too, is the evidence of sense-perceptions with regard to all testimony that implies the process of induction; e.g., I have only mediate evidence by my sight of the distances of objects; for any judgment I pronounce on that subject is derived from observation and induction united.

153. Authority gives us certainty in a still more circuitous way; for it brings us into communication with truth by means of the statements of other persons. The truth thus reached is said to be believed, and authority is called an extrinsic motive of certainty. Belief, or faith, is Divine or human, according as the authority on which it rests is Divine or human. In Philosophy we are concerned with human faith; and the question to be now considered is, whether the authority of human witnesses can be relied upon to give perfect certainty.

154. Thesis XIII. The testimony of men, under proper conditions, can give perfect certainty.

The conditions required are: 1. That the facts testified to are sufficiently open or accessible to observation; 2. That they are of great moment; else they might not be noticed carefully; 3. That the witnesses are sensible men; 4. That they are either undoubtedly sincere, or, if not, that they are many, of sufficiently different characters, opinions, parties, interests, etc., to exclude all reasonable suspicion of collusion in the support of false statements.

Proof. That testimony gives perfect certainty which convinces us beyond all reasonable doubt that the witnesses could not have been deceived themselves and did not wish to deceive us. But such is the testimony which fulfils the conditions just stated. For: 1. The witnesses could not have been deceived, since: (a) The facts are supposed to be open, accessible to observation; (b) They are of great moment, so as to invite careful examination; (c) The witnesses are sensible men, who do not act rashly and are not easily imposed upon; and, besides, they are of different opinions, characters, etc., so as not to make a mistake in common.

2. They do not wish to deceive us, since either they are known for certain to be sincere, and, of course, such men do not wish to deceive; or, if not certainly sincere, they are supposed to be many, of different characters, opinions, parties, interests, etc. Now, sensible men do not lie wantonly, especially on matters of importance; and, least of all, would they combine to propagate an important falsehood, unless some common grave interest led them into so disgraceful a crime. But they are supposed to have no such interest in common. There is, consequently, no reason to doubt their testimony.

155. Objections: 1. Each witness gives only probability, and no number of probabilities can make up certainty. Answer. Even one witness who is certainly intelligent, prudent, and sincere may give perfect certainty; but if the testimony of one or several still leaves special reasons to doubt, the testimony of others may show that the doubt is unfounded in the present case; certainty is thus attained, not by an accumulation of probabilities, but by the elimination of all motives for reasonable doubt.

2. Every witness is free to deceive. Answer. We can know from the conditions laid down that, in a given case, there was no actual attempt at deceit. Every man is free to commit suicide, and still it is certain that they will not all do so.

3. History contains many falsehoods. Answer. We do not defend all history.

4. At least, we cannot be certain of events long since past, because traditions are gradually changed. Answer. We can often be certain of such events, viz., when we know that, in a given instance, the tradition was not changed; e.g., we know for certain that Christ died on a cross; that He rose again; that His disciples preached His Resurrection; that they had no motive to do so if He had not risen; that they laid down their lives in testimony of their sincerity, etc. (See this argument more fully treated in Schouppe's Course of Religious Instruction, p. 6.)

5. At least, no amount of testimony can make miracles certain; for it is physically certain that they never occurred, while it is at most only morally certain that they did. Answer. It is not physically certain that they never occurred; all that is physically certain is that nature has no power to produce them, but the Lord of nature has; and it is morally certain that they have occurred.

6. Still, plain men could not assure us that any particular miracle was performed; for they are not fit judges of what is miraculous. Answer. Sensible men, even though unlearned, can give reliable testimony about obvious facts, of which learned men will judge whether they were natural or beyond all natural power.


156. There are many unwavering judgments or convictions common to all men of sound minds; all these may in a wider meaning be called dictates of common sense, i.e., of that sense or intellect which belongs in common to all men. Some of these judgments proceed from the testimony of consciousness, others from the immediate intuitions of identity between two ideas, others from intellect and sense-perceptions combined, others are the obvious deductions of reason from intuitive principles and from the perceptions of the senses. But the term common sense, when considered as a special motive of certainty, is taken in a more restricted meaning; it comprises those judgments only, common to all sensible men, which are not immediately or intuitively evident, and which are concerned with the direction of moral conduct.

157. The following are examples of common-sense judgments: "There is a sovereign Lord and Master of all things," "His Providence directs human affairs," "We must reverence Him," "We must obey His laws," "He is the rewarder of good and evil," "Our soul will survive our body," "There are rewards and punishments after death," "Children must honor and obey their parents," "Friends must help each other," "Brutes may be killed for the use of man," "Men cannot be killed without just cause," etc.

158. To find how far the judgments of common sense are reliable, we must carefully consider whence they proceed and what evidence they give us of the objective truth. We should not suppose that they proceed from the universal consent of men; men agree because each of them individually forms the same judgments, but each one separately does not form them because all agree: universality is a character, not a cause of them.

159. True, we may accept a judgment on the authority of men if their united testimony is known to us; but we are then influenced by another motive of certainty, viz., common consent. Thus, we may believe that man is fallen from an originally happier condition, because most nations have traditions to that effect; but the judgments of common sense are very different, being formed by each one independently of the consent of others.

160. Nor should we suppose that the judgments of common sense proceed, as Reid and his followers of the Scottish School maintain, from a mere instinct to believe certain truths. These writers wished to refute the Scepticism of Hume by the weapon of common sense; but they failed to establish the reliability of common sense by making it a mere blind instinct.

161. Whence, then, do the judgments of common sense derive their validity? From the evidence of the objective truth, which is presented with sufficient clearness to every sound mind. The objective truth in such cases is not intuitively beheld; we do not see immediately God's existence, nor the action of His providence, nor the soul as surviving the body, nor one being called virtue and another vice; but, starting with premises supplied by sense-perceptions and intellectual action, we go through an obvious process of reasoning, of which the evident conclusions are the dictates of common sense. For instance, my senses seize upon the fact of the world's existence, my intellect sees there must be a reason for its existence; and, not finding that reason in the world itself, my mind concludes by an obvious process of reasoning that there is a first cause of the world, distinct from it; besides, since we also understand that a thing made belongs to its maker, we conceive the Cause of this world as the Sovereign Lord and Master of all things, etc. The judgments of common sense, therefore, are reliable, because they are evident conclusions derived from evident premises.

162. This motive of certainty is, then, not entirely distinct from the motives already considered; but it has a special advantage, viz., that it furnishes us with a summary proof of many most important propositions, the detailed study of which would require lengthy explanations.

163. Thesis XIV. The judgments of common sense are true.

Proof. According to the principles that underlie inductive reasoning (No. 47), any constant, uniform, and unvarying effect produced by any class of objects must proceed from the very nature of those objects; but these judgments are constant, uniform, and unvarying in man; therefore they have for cause the very nature of man: in other words, it is natural or essential to man to form these judgments. Now, it cannot be natural or essential to man to form false judgments; else universal doubt would follow, which, however, has been proved to be absurd; therefore these judgments are not false, but true.

164. Objections: 1. Such judgments may have come from tradition, education, prejudices, human laws, etc. Answer. The effect cannot exceed the cause: all these causes are variable among men, except just so far as they can be traced to the very nature of man. Besides, mere traditions, etc., would not impose on the consciences of all so stern a sense of duty as belongs to the dictates of common sense.

2. These judgments might come from the passions of men. Answer. On the contrary, our passions would rather prompt us to deny these very judgments.

3. Huxley says that religion has been developed from men's instinctive belief in ghosts. Answer. Huxley's theory is, as usual with him, a mere theory unsupported by valid proof. The very fact that so determined and able an opponent of religion cannot adduce any more plausible theory to account for the conviction of mankind, is a strong presumption in favor of our thesis.

4. Ignorant men cannot reason well enough to form such judgments; therefore they only receive them from others. Answer. The reasoning in question is not difficult, but easy and obvious; though it is not pretended that every mind can give a philosophic account of its own reasonings.

5. Even great geniuses do not always see those conclusions. Answer. Geniuses often strive after originality of thought more than after truth, in order to make themselves a name; proud minds disdain to follow the beaten path, simply because it is the beaten path. (See further Metaphysics, No. 225.)

{1} Physiologists now split up the touch into two senses, the tactual or skin sense and the muscular sense; the former perceives heat and cold, roughness and smoothness, etc.; the latter perceives resistance, exteriority, and extension. President McCosh describes it thus, quoting Wundt's Beiträge zur Theorie der Sinneswharnehmung: "When we move our members we come upon external resistances. We observe that these resistances sometimes give way before our pressure: but at the same time that this takes place with very different degrees of facility, and that, in order to put different bodies in motion, we must apply very different degrees of muscular force; but to every single degree of the contraction-force there corresponds a determined degree in intensity of the muscular sensations. With tbese muscular sensations, the sensatians of the skin which cover our members of touch so continually mingle, that the intensity of these touch-sensations goes parallel to the intensity of the accompanying muscular sensations. We succeed in this way in connecting the degree of intensity of the muscular sensations in a necessary manner with the nature of the resistances which set themselves against our movement" (Defence of Fundamental Truth, p. 173).

{2} The objective reality of both sense-perception and intellectual perception is well expressed in the following words of very Rev. I. T. Hecker (Cath World, Oct., 1887, p. 6) " To see, if one is not a fool or a lunatic is to see something. To act on any other view of human life, is to tend to imbecility. This law of objective reality applies to the entire realm of human activity. Life is real. 'wherefore,' says St. Augustine on the Trinity (book ix), 'it must be clearly held that everything whatsoever that we know begets in us the knowledge of itself, for knowledge is brought forth from both, from the knower and the thing known."

{3} Hume writes in his Treatise on Human Nature: 'I dine, I play a game of backgammon, I converse and am happy with my friends and when, after three or four hours ot amusement, I would return to these speculations, they appear so cold, so strained, and so ridiculous that I cannot find it in my heart to enter into them any farther" (vol. i. p. 467). Why did Hume and Fichte write books if they really believed that no readers existed?

{4} See The Old Philosophy and Relativity of Knowledge by Henry Brown. (The Month, September, 1888.)

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