ART. I. -- HYPOTHESIS.
105. Hypothesis is a probable assumption which is intended to explain the cause and nature of a fact, but is not as yet verified by experience or demonstrated by reason. -- The mind often cannot ascertain with certainty the reason of facts; it then finds it necessary to adopt conditionally a principle that is probable. If experience and reason afterwards verify this principle, it ceases to be a supposition or hypothesis, and becomes a thesis.
106. In all the sciences hypotheses within certain limits are useful; in all the natural sciences they are necessary. -- Some philosophers maintain, with Reid (1710-1796), that hypotheses must necessarily be detrimental to science. This is an assertion contradicted by good sense and experience. Others, like Condillac (1715-1780), admit the use of hypotheses in the mathematical sciences only. But it is evident that, with the greatest philosophers and naturalists, we ought to admit them, at least within certain limits, in all the sciences, since in them there are facts not yet explained and for the explanation of which we may very conveniently resort to hypotheses, which subsequent observation will often transform into certain and scientific principles. But hypotheses are useful only in so far as they conform to certain laws; otherwise they are hurtful, and, by originating false systems, are fruitful sources of error.
107. Hypotheses are subject to two sorts of rules, one regarding the formation of the hypothesis, the other its verification. -- The rules to be observed in the formation of an hypothesis are three: 1. It must rest on the knowledge of a great number of facts; 2. From among the circumstances which accompany a fact we should select one or more, and see if they do not suffice for the explanation of the fact; 3. The circumstances selected ought to be such as to account for all the others.
There are four rules to be observed in verifying an hypothesis: 1. It should not be opposed to the fact which it is intended to explain; 2. It should be such as to explain all the facts for which it has been made; 3. An hypothesis supported by certain facts should be preferred to one not supported by any fact; 4. From among the hypotheses presented we should choose the simplest. It is evident that if an hypothesis conflicts with a truth known as certain, it is, by the fact, proved false.
ART. II. -- EXPERIMENTATION.
108. Experimentation is the act or art of producing or modifying at will the phenomena of nature in order to study them. -- In all the sciences, and especially in the physical or natural sciences, it becomes necessary to make an attentive study of the phenomena of nature. The more easily to account for these phenomena, we modify or produce them at pleasure; this process is called experimentation. If we confine ourselves to studying a phenomenon as presented in nature, we simply make an observation.
109. The conditions of good experimentation relate, some to what is produced in the phenomenon, others to the person who experiments. -- In regard to the phenomenon, it is necessary to keep an exact record of all the accompanying circumstances, however minute; and when it can be done, these circumstances should be noted by figures and exact quantities. The person who is experimenting should (1) vary the experiments; (2) extend them; (3) reverse them. Above all, he should guard in experimentation against the spirit of system, which would make him see not what is, but what he wishes should be.
110. As experimentation is employed to determine the cause of a phenomenon, we must carefully look out for indications which may point to the cause. -- These indications are four in number: 1. When one event invariably precedes another, except when the latter is counteracted or prevented by some circumstance; 2. When, one event undergoing a modification, another undergoes a corresponding modification; 3. When, one fact being absent, another is also absent, unless the latter may also be produced by a different cause; 4. When, one fact disappearing, another also disappears, unless the latter can exist without the continued action of the former.{1}
111. Experimentation of itself does not constitute science; it only enables us to establish principles by induction. -- As experimentation does not go outside the order of facts, it cannot of itself constitute science; but when well conducted, it enables us to establish principles of experience, as, "Water slakes thirst." These principles, to be such, must fulfil two conditions: 1. The fact which we wish to transform into an experimental principle must have been found the same in many cases; 2. This fact must not be accidental, but a natural effect.
112. Having by experimentation discovered points of agreement among several objects, we are enabled by the principle of analogy to infer other points of agreement: experimentation thus abridges scientific investigations and even makes up for impossible investigations. -- When several objects are known to agree in certain points, the principle of analogy enables us to conclude other points of agreement. This conclusion may be based either upon the simple relation of qualities, or the relation of means to an end, or the relation of cause to effect or effect to cause. But it can be considered legitimate only inasmuch as it rests not upon fortuitous or accidental resemblances, but upon important resemblances, or, in the absence of these, upon many resemblances.{2}
ART. III. -- CLASSIFICATION.
113. Classification is the distribution of entities into genera end species. -- In every science it is necessary to proceed with order both in the discovery and in the communication of truth; in this sense, then, classification is requisite in every science. But the term is especially applied to the distribution into genera and species adopted in natural history.
114. The advantages of this classification are: 1. It aids the memory and facilitates the knowledge of the objects classified; 2. It in a way initiates us into the divine plan, by showing us the admirable order which reigns among all creatures. -- Classification, by the fact that it puts order into the objects which we study, enables us to know them better and to apprehend their relations but, above all, it elevates the mind, by enabling it to penetrate the admirable harmony of the divine plan. This last result can be obtained only in so far as the classification is based upon nature itself. An artificial classification serves only to put a certain order into our knowledge, and is not in itself of any scientific value.
115. The laws of classification are: 1. It must be complete; 2. It must be based on the law of the subordination of characteristics. -- Evidently the first condition requisite for a good classification is that it comprise all the objects for which it is made. But it is also necessary, if we desire a natural or scientific classification, to base it on the law of the subordination of characteristics. In virtue of this law objects in nature have each a primary characteristic, to which other secondary characteristics are subordinate; to these latter still others are subordinate, until we finally reach the least important characteristic. We classify according to this law when we establish the principal divisions according to the principal characteristics, then subdivide according to subordination of characteristics. It is easily seen that such a classification is nothing else than the science of the objects classified. Hence, if we know to what division an object belongs, we immediately know its nature and characteristics.{3}
The great progress made in the natural sciences since the Reformation by the application of the experimental or a posteriori method has led many of its advocates to bring the same method into the field of philosophy in its different divisions and of theology. But such a proceeding has invariably been followed by results not only most disastrous to all positive religion, but even suicidal to human thought. The Church is the "pillar and ground of truth," and has nothing to fear and much to gain from the daily advances of scientific research. "Grammar, philology, archaeology, history, ethnography, erudition, topography, aesthetics, all that makes up the long line of rationalistic criticism, have in turn paid her a forced homage."{4} The well ascertained results of science, the well-founded hypotheses, are all in harmony with her teaching. But when any rash conclusion is foisted on the public, the divine guardian of the truth sounds the alarm.
{1} Compare these indications with the following experimental methods of John Stuart Mill (1806-1873): (a) Method of Agreement. -- "If two or more instances of the phenomenon under investigation have one circumstance in common, the circumstance in which alone all the instances agree is the cause (or effect) of the given phenomenon." (b) Method of Difference. -- "If an instance in which the phenomenon under investigation occurs and another in which it does not occur have every circumstance in common save one, that one occuring only in the former, the circumstance in which alone the instances differ is the effect, or the cause, or an indispensable part of the cause of the phenomenon." (c) Method of Concomitant Variation. -- "Whatever phenomenon varies in any manner whenever another phenomenon varies in some particular manner, is either a cause or an effect of that phenomenon, or is connected with it through some fact of causation." (d) Method of Residues. -- "Subduct from any phenomenon such part as is known by previous induction to be the effect of certain antecedents, and the residue of the phenomenon is the effect of the remaining antecedent." -- Mill's Logic.
{2} See Logic, § 64.
{3} See Metaphysics of the School, vol. ii., pp. 508-514, 515, 584.
{4} Apologie Scientifique de la Foi Chrétienne, by Canon Duilhé de Saint-Projet, p. 105.