1. Psychology is a science which treats of the human soul, its faculties, its properties, and its relations with the body. -- Man is, as it were, a compendium of all creation; for in him are found being, life, sense, reason, and corporeal nature united to spiritual nature. Therefore the study of man specially pertains to philosophy. That part of philosophy which treats of man is called Psychology or Anthropology. The name psychology more particularly signifies the study of the soul; but because it is almost impossible to know the soul rightly without considering it in its relations with the body, it is necessary for psychology to study the whole man.
2. The method to be followed in psychology is analytico-synthetical, a method that joins observation to reason. -- Some philosophers, as Bacon, Locke, Reid and his disciples, admit only the experimental method in psychology; but this method can never give psychological science, because it regards only facts; it cannot, therefore, solve problems concerning the essence, origin, and end of the soul. Other philosophers, as Schelling and Hegel, hold that the science of man should be constructed a priori; but this method is also false, because by observation the operations of the soul are known, and by reasoning, its nature. Hence it is by observation together with reasoning that the philosopher should construct the science of psychology.
ART. I. -- FACULTIES OF THE HUMAN SOUL.
3. The human soul has vegetative, sensitive, and intellective faculties. The sensitive and intellective faculties are divided into cognitive and appetitive faculties. -- Since the human soul has vegetative, sensitive, and intellective life, it must have the faculties of these three kinds of life. Cosmology treats of the faculties of vegetative life, but only in a general way, leaving to subordinate sciences the psychological investigation of these faculties. Rational Psychology treats of the sensitive and the intellective faculties, but in the consideration of the former omits the physiological development of their organs, which belongs properly to Empirical or Physiological Psychology. Both the sensitive and the intellective faculties are primarily passive, since they must first be acted upon before they operate; but they are also secondarily active, because they are vital powers. Strictly speaking, a power is active when it modifies, or, so to say, makes its object, and of this kind are the vegetative faculties; it is passive when it must be acted upon and moved by its object; and such are the senses and intellect. A faculty, whether sensitive or intellective, is called cognitive, when it can know an object; it is appetitive, when it tends to union with the object known.
4. In the cognitive faculties the object known shares in the perfection or imperfection of the subject knowing; in the appetitive faculties the subject shares in the perfection or imperfection of the object to which the faculties are directed. -- The object of a cognitive faculty assumes the conditions of the subject knowing before its union with that subject. A stone in its physical reality is material; but when it becomes known by the senses, it has in them an immaterial existence; a circle is always united to matter in the real order, but when abstracted by the intellect, it has not only an immaterial, but a universal existence. But as objects inferior to the subject knowing receive a new perfection when by cognition they exist in the subject, so objects superior to it share in its imperfection in so far as they are objects known. It is far otherwise with the appetitive faculties: through these the subject acted upon tends to union with the object, and in a certain sense to be transformed into it; through these, therefore, the subject shares in the perfection or imperfection of the object. The soul, for instance, is elevated by union with the will of God, but is degraded by attaching itself to creatures.
ART. II. -- THE COGNITIVE SENSITIVE FACULTIES. -- SENSIBILITY IN GENERAL.
5. Cognition in general is an operation by which a living being perceives itself or some object present to it. -- By cognition in general a living being perceives and discerns itself, or some object present to it. Since cognition is wholly contained within the subject knowing, it follows that it becomes aware of external things in so far as they are in some way present within it. But external things cannot in their own nature enter the subject knowing, but solely through the medium of certain forms representing them and called intentional species.{1} It is, therefore, by these species that things are known.
6. The senses are passive powers by which the sensitive being perceives sensible objects. -- The senses are passive powers, because they do not act until some sensible object has determined them to act, and principally because they do not form their object, but are informed by it. By them the sensitive being perceives all that is comprised under the name of sensible object. This perception is called sensation.
7. The senses are classified as external and internal, according as they perceive external objects or the modifications produced in the sensitive subject. -- The action of the external object on the sentient subject produces a modification in the sense, and thus determines it to perceive its object. By the internal senses the subject perceives its external sensations.
8. The senses, both external and internal, 1. reside in a corporeal organ; 2. cannot reflect on their sensations; 3. can have nothing but what is material for their object. -- 1. The senses, as is attested by experience, are moved to act by corporeal objects. But what is corporeal cannot act on the senses, if they are not themselves corporeal yet vital, that is, organic. For bodies must act according to their nature and can produce only a material modification, since otherwise the effect would exceed the power of its cause; but the senses could not receive this modification if they had not a material organ. No sense, therefore, can be without an organ fitted to receive the material impression which is produced by an object external to it, and which determines the sense to act. This material organ, because informed by the soul, can serve the soul in the act of sensation. 2. No sense can reflect on its own operation, because a faculty cannot reflect on its own action, unless it wholly and entirely return upon itself. But this is impossible to the senses, for they depend on material organs, one part of which might indeed return upon another part; but what is extended can never in its entirety return upon itself. 3. Since every sense consists of a material vital organ, it must necessarily have something material for its object. This is equally true of the internal senses, for they are put into exercise by sensations received through the external senses and accompanied by a material modification. Thus, although the object of internal sensibility is not absolutely material like that of external sensibility, yet it has in it something material that enables it to reduce the internal senses to action.
9. The cause of sensation is not the mere activity of the soul, as was held by Leibnitz and Fichte. -- Leibnitz maintained that the soul is the only and necessary cause of sensation. But if the soul has sensations necessarily, evidently it must have them always, an assertion which is contradicted by experience. Besides, if the soul alone has sensations in virtue of its nature, how does this nature which is ever the same, become sensible of things which are contrary to one another or which have no bond of union? How, if it is sentient in itself alone, can it by sensation perceive bodies outside itself? Let it not be said that the presence of the external body is necessary as the condition or occasion of sensation; for, either the body does not of itself really determine the soul to sensation, and then its presence is useless; or it does of itself determine the soul to sensation, and then the soul is not the only cause of sensation.
Fichte, while admitting the soul to be by itself alone the cause of sensation, considered it not a necessary, but a free cause. But this is plainly contradicted by experience, which shows us that our sensations do not depend on our will; that, on the contrary, we often experience sensations which we would wish not to have, and are deprived of otbers that we desire.
10. The only cause of sensation is not, as Berkeley asserted, the action of God on the soul. -- Berkeley (1684-1753) taught that the soul, being immaterial, could not be affected by the action of a material object, but that since the representations of bodies in the faculties of the soul are an undoubted fact, they cannot otherwise be explained than by the action of God on the soul; he added that only spiritual beings exist, and that bodies are but a simple succession of ideas formed in us by God. This theory is evidently erroneous, for, were it true, God would be constantly deceiving us by creating within us representations of bodies that do not exist. Should any one insist with Malebranche, that God by His omnipotence can produce in us the perceptions of bodies, although the bodies do not exist, then would the omnipotence of God be placed in contradiction to His veracity, and God Himself would be made contradictory. Besides, in this system it is absolutely impossible to account for the diversity of sensations among men in reference to the same object, as also to explain the connection that exists between certain sensations; for example, between the sensations produced by an animalcule according as it is or is not seen under the microscope. Lastly, this system is based on the principle that "like can be known only by like." But this principle is manifestly false,{2} for in accordance with it materialists could deny the existence of spirits, since the perception of matter is incontestable; and idealists might question the existence of bodies, since the nature of the soul is immaterial.
11. The only cause of sensation is not, as materialists maintain, the impression of the material object on the sentient subject. -- Broussais held that the impression constitutes the whole sensation, and regarded the brain as the sentient subject. Now, the brain is material, and what is material is composed of parts distinct one from another. If, therefore, what is material has sensations, we must conclude that each part has either the whole sensation or only a part of it. In the former case, there would be as many sensations as there are parts in the sentient subject; in the latter, the sensation would never be entire, for each part would have for itself only that part which it had received. Now, on the one hand, experience attests that sensation is one and indivisible, and, on the other hand, that in its indivisible unity it represents the entire sensible that is its object.
Cabanis (1757-1808), while agreeing with Broussais (1772-1838) that the impression constitutes the whole sensation, regarded the soul alone as the subject of sensation. But this cannot be, for the sensible object can produce an impression only on the organ; but sensation is something very different from this purely material impression. Sensation results from the action of the sense, whereas the impression is passive.
12. Sensation is produced by two causes: tbe material object and the activity of the sense. -- There can be no sensation if the activity of the sense is not exercised; but, since the senses have a material object for their term, it must be this object that calls forth their action. Hence sensation is both active and passive; it is passive in so far as it presupposes the action of a sensible object; it is active so far as, given this action, sensation follows from the activity of the sentient subject.
13. The sensible object is joined to the sentient subject by means of a certain representation of itself which is called the sensible species. -- Sensation is an immanent action which is produced in the sentient subject, is proportioned to it, and remains wholly within it; but it does not take place without a material object which acts upon the sentient subject, and is perceived or cognized by it.
For the production of sensation, the material object must in some way be joined to the sentient subject. But evidently it cannot enter in its physical reality; it must, therefore, enter through something which represents it; and this is called the sensible intentional species. This sensible species produced by the object is not a simple excitation which is caused in the sensitive faculty by its contact with the object; but, since it makes known the object, it is necessarily a representation of it which renders it present to the sensitive faculty. Thus the image formed on the retina of the eye by a body is not merely a motion, an excitation, which leads the sight to perceive the body, but it is a representation of it by which it is conjoined to the sense of sight.
14. The sensible species is not the object of sensation, but the medium by which sensation is effected. -- The sensible species in the subject knowing is the immediate principle that determines the act of sensation; hence it could not be perceived by the sensitive faculty except by a reflex act, which sense cannot perform. Now, not only does reflex action suppose a previous act, but it cannot even be effected by the senses. Therefore the sensible species is not that which the sense perceives; it is the medium by which the sense cognizes its object. While it informs the sense, the object is perceived; if, then, for any cause it remains in the sense, though the object be absent, perception will be had just as if the object were present, as is the case with the insane.
15. Between the sensible species and sensation there is a relation of causality. -- The sensible species is not sensation, but it determines the act of sensation, so that the senses do not act unless determined by the sensible species. When, however, this determination has been effected, the senses must act and thus perceive the object that impressed them. Hence a relation of causality exists between the sensible species impressed and the sensible species expressed, or sensation.{3}
ART. III. -- EXTERNAL SENSIBILITY IN GENERAL.
16. The object of the external senses is the external sensible which is present to sense and suitably disposed. -- The external senses are those to which the species of external objects are referred; hence they have material external things for their object. But this object must be present; for only the Internal senses can preserve sensible species, and, consequently, they alone can apply themselves to absent things. Finally, the object should also be suitably disposed, otherwise it could not impress the sense, that is, form in it the sensible species.
17. There are three kinds of sensible objects: the proper, the common, and the accidental. -- Of the qualities of bodies which we perceive, some are perceived by one sense only, as "color" by the sight, and these are called proper sensibles. Others are the object of several senses, as "figure," which is perceived by both sight and touch, and these are common sensibles. Others, again, are not perceived directly, because they are implicitly contained in the sensible qualities, as "substance," and these are accidental sensibles. There are five kinds of proper sensibles, the objects respectively of the sight, the hearing, the smell, the taste, and the touch. There are likewise five kinds of common sensibles: "motion, rest, number, figure, and dimension." To these five common sensibles, "time, posture, unity, distance, and proximity," are referred. The accidental sensible is whatever is implicitly contained in the sensible appearance, and as it were naturally connected with it: as "anger, love, hatred," etc. The proper sensible impresses the species, the common sensible modifies this; thus each is represented by its own species, one unmodified, the other modified. The accidental sensible neither impresses nor modifies a species; it is merely connected with the objects represented by the species, as with natural signs.
18. Some senses need a medium through which they receive the species impressed. -- Sensitive knowledge is attained only by means of a species which represents the object in the sentient subject. In some of the senses the production of the species is not aided but hindered by contact of the object with the organ of sense. Thus, for instance, an image of the object is not formed on the retina when the object touches the eye.
19. When the senses act in their normal condition, they do not deceive us as to their proper sensibles; but they may become an occasion of error as to common or accidental sensibles. -- Nature has given us senses that they may each make known to us their proper sensibles; hence they cannot deceive us as to these sensibles unless there is some defect in the organ, or the sensible is too distant, or the medium is accidentally modified. But as nature has not charged one sole external sense to cognize the common sensible and the accidental sensible, a single external sense may deceive us in regard to these sensibles. Thus, in perspective, the eye deceives us in regard to the common sensible, distance. That the common sensible may be known with certainty, it must be known through the concurrence of several senses.
20. Proper sensibles actually perceived by the external senses, are only virtually in bodies; they are actually in subject. -- Taste, smell, and the other proper sensibles are not actually in bodies as they are in the senses, otherwise the bodies would have sensations. They exist actually in the sentient subject only. Thus the sweet or bitter is a modification of the organ of taste, in consequence of which it experiences the sensation of sweetness or bitterness. Yet, although these qualities which are called proper sensibles are not found actually in bodies, they exist in them virtually, since bodies really have qualities by which they are apt to produce corresponding sensations in the organs of sense. Thus bodies are not sonorous, savory, or odoriferous; but they are apt to produce in our senses the sensation of sound, of taste, or of smell.
21. The object of external sensation consists primarily and immediately in sensible qualities, but mediately and secondarily in the subject in which the qualities exist. Hence the external senses perceive bodies through the medium of their proper sensibles which exist in the bodies. -- Sensible qualities or sensibles are not, as some affirm, mere modifications of the organs of sense, but the object perceived by sense. But since the senses cannot perceive their own perceptions or sensations, being organic faculties, these must be perceived by the internal sense called common sense (sensus communis). As inhering in a substance, sensible qualities are perceived by the external senses. But as they cannot exist apart from the bodies of which they are qualities, the senses cannot apprehend them apart from their subject except by the process of abstraction; but of this act they are incapable, for they are organic faculties. Therefore they must apprehend the sensible qualities in the corporeal subject in which they exist; but this is equivalent to saying that they apprehend both the qualities and their subject, though not in the same way. The qualities are their proper object; the substance, their object per accidens. From this two consequences follow. The first is that the external senses perceive bodies by perceiving their qualities. By the sense of sight we do not become cognizant of the impression made in the sense: this is known to be there by reason; while common sense, or sensitive consciousness, perceives the sensation; but by the sight we perceive color, and through it the colored body other than ourselves. The second consequence is that the perception of bodies is immediate, but not per se, but per accidens; because, the external senses requiring the qualities of bodies in order to perceive bodies themselves, this perception takes place indirectly.
22. It is erroneous to hold with Uondillac that sensations being mere modifications of the sentient subject, the soul has no perception of an object other than itself except through the medium of touch. -- The philosophers who have denied that the external senses perceive bodies immediately, have been compelled to seek by what means the soul perceives an object distinct from itself. Condillac, starting with the hypothesis of the "man-statue," says that so long as this statue is endowed with only the senses of sight, hearing, taste and smell, it perceives nothing more than that it is itself affected in this or that way; but when the statue moves and by active touch feels something that resists it, it then perceives an object distinct from itself, and is led to believe that the perceptions of the other four senses also relate to an object external to the sentient subject. Thus the touch would be a medium by which the soul would pass to something distinct from itself.
It is easy to see the absurdity of such a theory to explain the perception of bodies. Besides, it rests on an hypothesis essentially contradictory. For according to this theory bodies produce sensations, and the sensations produce the sensitive faculties. But on the one hand, sensation must be elicited by a sentient subject; on the otber band, sensation, far from producing the sensitive faculty, supposes its existence.
23. We cannot admit with Reid, that the soul cognizes bodies by means of certain instinctive judgments. -- Reid, like Condillac, holds that the senses do not perceive bodies, but merely the sensible qualities, and that moreover sensation is purely subjective; for, he tells us, as soon as the senses have perceived the sensible qualities, the intellect pronounces this instinctive judgment: "There are no sensible qualities without an existing material subject." But if this judgment is instinctive, it proceeds from the natural constitution of the soul, and consequently is purely subjective. But a purely subjective judgment applied to subjective sensations cannot manifest an objective reality.
24. We cannot admit, with Fichte, that the soul perceives bodies, not as objective realities, but as representations which the soul forms at will within itself. -- Deducing the ultimate consequences of the subjectivism of Kant, Fichte holds that when the soul perceives bodies, it perceives nothing more than its own representations formed by an exercise of its will. This theory is essentially absurd and contradictory. For the will cannot be the cause of the representation of bodies; it cannot will their representation unless they be already known. Besides, if the representation of bodies is purely the effect of the will, why is it that the soul cannot experience at will a sensation that it desires?
25. It is false to assert with Cousin that sensation is purely subjective, and that from it the soul infers with the aid of the principle of causality that bodies exist. -- With these two premises. viz., sensation is an effect, and every effect must have a cause, we can draw no conclusion but that sensation must have a cause. But there is nothing to assure us that this cause is the body, or, as Berkeley maintained, God Himself.
ART IV. -- THE EXTERNAL SENSES IN PARTICULAR.
26. The external senses are five in number: Sight, hearing, smell, taste, and touch. -- A sensitive being must have as many senses as are required for the preservation of its existence. But for this five senses are necessary; for by means of sight it perceives the disposition of the surrounding objects; by means of hearing, the motion of those which it does not see; by means of smell, it perceives the character of the aliments that are not yet within its reach; by the taste it judges of them with more care before taking them as food; lastly, by the touch it oversees the state of its own body and its relation to external things. These five senses should be found in every perfect sensitive being. -- Again, our senses are five, because there are five formally distinct material objects to be cognized, viz., the different qualities of bodies; and our senses are given to us for such cognition.
27. Among the five senses, sight is the most intellective, touch the most necessary. -- Sight is the most intellective sense, that which plays the chief part in the cognition of bodies: for its exercise it requires only light, the most subtile of material things. Hearing, although in itself inferior to sight, yet possesses two advantages over it: the first is that it perceives sounds from every direction; the second is that it operates even in the absence of light. Hearing is the sense most important to man, for it is especially through it that the intellect acquires the cognitions necessary to its natural development. And divine faith comes by hearing. Smell perceives even an absent body by means of the emanations which it sends forth, and thus it informs us where bodies are when sight and hearing fail. This sense is necessary to the animal to find food; it is useful to point out what food is suitable for it and what is not. Taste is a sense distinct from touch, its organ being the tongue in connection with the palate; for savor differs formally from the other tactile qualities; and their objects specify the faculties. Touch is a sense having its organ in the whole body, especially the ends of the fingers. Its purposes are manifold. This is the most material of all the senses; it is also the most necessary to animal life. To preserve life, the animal must by the medium of touch guard against what can harm its body, just as by the taste it must perceive what food is proper for the support of its body.
{1} They are named species, because they are likenesses or forms of the object they are called intentional, either because they intend, as it were, to represent the object, or because they tend from the object to the various faculties that receive the impressions. -- See Sum. Th., i., q. 78, a. 3.
{2} This principle must not be confounded with the principle of assimilation in the Scholastic theory of cognition "Whatever is received is received according to the nature of the receiver." It follows from this principle that all objects known are in the act of cognition, which is an immanent act, assimilated to the subject knowing.
{3} These vicarious species, considered as acting on the sense, were called impressed species; considered as actually received into the sense, as informing it, and producing a corresponding reaction which we call sensation, they were termed expressed species; "their intention being thus far realized."