But, secondly, what is the real case? To proceed à priori is to argue from the cause to the effect, and from antecedents to consequents; whereas, to proceed à posteriori is to argue from the effect to the cause, and from consequents to antecedents. Now, it is a fact that in metaphysics we frequently argue from the cause to the effect, as is done in other sciences too; but it is no less a fact that we even more frequently argue from the effect to the cause. The very name of metaphysics, which is the bugbear of our opponents, clearly shows that such is the case. Real philosophy, in fact, is called metaphysics for two reasons, the first of which is extrinsic and historical, the second intrinsic and logical. The historical consists in the fact that Aristotle's speculations on those incomplete entities which enter into the constitution of things were handed down to us under the name of metaphysics. The logical is, because the knowledge of such incomplete entities must be gathered from the consideration of natural beings by means of an intellectual analysis, which cannot be made properly without a previous extensive knowledge of the concrete order of things. This latter knowledge, which must be gathered by observation and experiment, constitutes physical science. Hence, the rational knowledge which comes after it, and is based on it, is very properly called metaphysical, and that part of philosophy which develops such a knowledge metaphysics—that is, after-physics.
Now, all analysis belongs to the à posteriori process; for it proceeds from the compound to its components, and therefore from the effect to the cause. Therefore, metaphysics, inasmuch as it analyzes natural beings and finds out their constituents, is an à posteriori science; and since such an analysis is the very ground of all metaphysical speculations, we must conclude that the whole of metaphysics is based on the à posteriori process, no less than physics itself.
Thirdly, that metaphysics cannot decide any matter-of-fact question is a silly objection; as it is evident that to establish the existence of God, the spirituality of the human soul, the creation of the world, etc., is nothing less than to decide matters of fact. It may be that, in the opinion of the utilitarian, such facts are not very interesting; they are facts, however, as much and as truly as the rotation of the earth, atmospheric pressure, and universal attraction are facts; and they are much more important, too.
We might also maintain that metaphysics is mainly a science of facts; for there are facts of the intellectual as well as of the experimental order. That every effect must have a cause is a fact. That every circle must have a centre is another fact. That a part is less than the whole is a third fact. Intellectual facts are as numerous and as certain as the facts of nature; and it is through them that our experimental knowledge of natural things is raised to the dignity of scientific cognition. For there is no science, whether inductive or deductive, without reasoning, and no reasoning without principles; and every principle is a fact of the intellectual order. Those critics who are wont to slight metaphysics as an à priori science would, therefore, do well to consider that no true demonstration can be made but by à priori principles, and that true demonstration constitutes the perfection of science.
We may here remark that metaphysics is usually divided into general and special, and that the à priori character, for which it is assailed, belongs to general metaphysics only. General metaphysics treats of the constituents, attributes, and properties of being in general, and is called ontology. Ontology is considered as a necessary preparation for the study of special metaphysics, which, from the knowledge of being in general, descends to the examination of the different classes and genera of beings in particular. Our men of science, accustomed as they are to the inductive method, do not approve of this form of proceeding. On what ground, they ask, do you impose upon the student notions, definitions, and principles à priori, as you do in ontology, affirming in general that which has not yet been examined in particular, and taking for granted what has yet to be established and verified?
The answer is obvious enough. General metaphysics assumes nothing but what is already admitted as evident by all mankind. It is mainly concerned with the notions conveyed by such words as being, cause, effect, principle, essence, existence, substance, accident, etc. These notions are common, and their methodical explanation is based on common-sense principles—that is, on evident, intellectual facts. Thus far, therefore, no one can say that we invert the natural order of science; for we start from what is known.
Next comes the analysis of the notions just referred to. The object of this analysis is to point out distinctly the different classes of being, the different genera of causes, the variety of principles, reasons, etc., implied in those general notions, to show their ontological relations, and to account for their distinction. This important investigation, as well as the preceding one, is based on common-sense reasonings, but sometimes not without reference to other truths, which are established and vindicated only in special metaphysics, to which they properly belong. Thus, it is the custom to treat in ontology of the intrinsic possibility of things, and its eternity, necessity, and immutability; but it is only in natural theology that such matters find their full and radical explanation. Of course, whenever an assertion is made, of which the proof is totally or partially deferred to a later time, the assent of the student to it is more or less provisional. It is not, however, in metaphysics only that a student must accept certain things on trust; he thus accepts the equivalents in chemistry, the distances of the planets from the sun in astronomy, and the logarithms in trigonometry.
Yet we confess that philosophical writers and teachers sometimes expose themselves to just criticism by treating in general metaphysics certain matters which it would be better to reserve intact for special treatises. It is doubtless necessary, immediately after logic, to treat of the nature of being, and its principles and its properties in general; but it is extremely difficult, and even dangerous, to undertake the settlement of some questions of ontology connected with the physical department of science before these same questions are sufficiently explored by the light, and disentangled by the analysis, of special metaphysics, to which their full investigation really appertains. What is the use of giving, for instance, an unestablished, and perhaps preposterous, notion of corporeal quantity to him who has as yet to learn what is the essential composition of bodies? Is a student prepared to realize the true nature of the quantity of mass, or of the quantity of volume, who has never yet explored either the mysterious attributes of formal continuity or the intimate constitution of material substance? Certainly not. He may, indeed, make an act of faith on the authority of his professor; but philosophy is not faith, and no professor who understands his duty would ever unnecessarily oblige his pupils to admit anything as true on his own sole authority. Questions connected with the physical laws of causation and movement, or with the nature of sensible qualities and properties, should similarly be deferred to a later time; for no one will be able to deal successfully with them, unless he has already acquired a distinct knowledge of many other things, on which both the right understanding and the right solution of these questions essentially depend. Accordingly, such matters, instead of being treated lightly and perfunctorily at the beginning of the course of metaphysics, should be treated with those others to which they are naturally allied, in order that they may be fully examined and competently decided.
From this it will be seen that we do not want a metaphysical science based on à priori grounds. In all times, metaphysics has been a science of facts; and it could not be otherwise, since its object is real, and all that is real is a matter of fact. Experiment and observation have always supplied the materials of its speculations. All its conclusions about the nature of the soul are drawn from the facts of consciousness; all its affirmations concerning the constitution of bodies are founded on the facts and laws of the physical world; and all its theses on God, his existence and his attributes, are likewise deduced from a positive knowledge of contingent things. To suppose that metaphysical knowledge can be obtained otherwise is such an absurdity that nothing but the most stupid ignorance can be made to believe it. And yet this absurdity is what many of our modern scientists fall into when they contend that metaphysics is an à priori science.
It is not difficult, however, to account for such a dislike of metaphysical reasonings. The greatest number of our scientific men have been brought up under the influence either of Protestantism or of its legitimate offspring, indifferentism; and absolute truth, such as is attained by rigorous metaphysical reasoning, is not congenial to their habit of thought. Protestantism is a system made up of half-truths, half-premises, and half-consequences. A Protestant must at the same time believe the authenticity of the Bible, and reject the authority by which alone the Bible can be proved to be authentic; he must conciliate the liberty of his private judgment with the obedience due to the teaching of his church; he must have the courage to believe that true Christian religion is not that which, from the apostolic times down to our own, has formed so many generations of saints, changed the face of the world, confirmed its own divine origin by a perpetual succession of prodigious works, but that which, starting from Luther or some other mischievous innovator, has never and nowhere produced any fruit of high sanctity or witnessed a single miracle. Hence, to a Protestant mind, truth in its entirety must be embarrassing; since the very essence of Protestantism is to cut truth into pieces, to believe and relish a portion of it, and to reserve some other portion unbelieved and unrelished, lest nothing should be left to protest against.