What has been called the Principle of Sufficient Reason asserts, when applied to reality, that every existing reality must have a sufficient reason for existing and for being what it is.[439] Unlike the Principle of Causality which is an axiomatic or self-evident truth, this principle is rather a necessary postulate of all knowledge, an assumption that reality is intelligible. It does not mean that all reality, or even any single finite reality, is adequately intelligible to our finite minds. In the words of Bossuet, we do not know everything about anything: “nous ne savons le tout de rien”.
In regard to contingent essences, if these be composite we can find a sufficient reason why they are such in their constitutive principles; but in regard to simple essences, or to the simple constitutive principles of composite essences, we can find no sufficient reason why they are such in anything even logically distinct from themselves: they are what they are because they are what they are, and to demand why they are what they are, is, as Aristotle remarked, to ask an idle question. At the same time, when we have convinced ourselves that their actual existence involves the existence of a Supreme, Self-Existent, Intelligent Being, we can see that the essence of this Being is the ultimate ground of the intrinsic possibility of all finite essences ([20]).
In regard to contingent existences the Principle of Sufficient Reason is coincident with the Principle of Causality, inasmuch as the sufficient reason of the actual existence of any contingent thing consists in the extrinsic real principles which are its causes. The existence of contingent things involves the existence of a Necessary Being. We may say that the sufficient reason for the existence of the Necessary Being is the Divine Essence Itself; but this is merely denying that there is outside this Being any sufficient reason, i.e. any cause of the latter's existence; it is the recognition that the Principle of Causality is inapplicable to the Necessary Being. The Principle of Sufficient Reason, in this application of it, is logically posterior to the Principle of Causality.[440]
95. Classification of Causes: Aristotle's Fourfold Division.—In modern times many scientists and philosophers have thought it possible to explain the order and course of nature, the whole cosmic process and the entire universe of our experience, by an appeal to the operation of efficient causes. Espousing a mechanical, as opposed to a teleological, conception of the universe, they have denied or ignored all influence of purpose, and eschewed all study of final causes. Furthermore, misconceiving or neglecting the category of substance, and the doctrine of substantial change, they find no place in their speculations for any consideration of formal and material causes. Yet without final, formal and material causes, so fully analysed by Aristotle[441] and the scholastics, no satisfactory explanation of the world of our experience can possibly be found. Let us therefore commence by outlining the traditional fourfold division of causes.
We have seen already that change involves composition or compositeness in the thing that is subject to change. Hence two intrinsic principles contribute to the constitution of such a thing, the one a passive, determinable principle, its material cause, the other an active, determining principle, its formal cause. Some changes in material things are superficial, not reaching to the substance itself of the thing; these are accidental, involving the union of some accidental “form” with the concrete pre-existing substance as material (materia “secunda”). Others are more profound, changes of the substance itself; these are substantial, involving the union of a new substantial “form” with the primal material principal (materia “prima”) of the substance undergoing the change. But whether the change be substantial or accidental we can always distinguish in the resulting composite thing two intrinsic constitutive principles, its formal cause and its material cause. The agencies in nature which, by their activity, bring about change, are efficient causes. Finally, since it is an undeniable fact that there is order in the universe, that its processes give evidence of regularity, of operation according to law, that the cosmos reveals a harmonious co-ordination of manifold agencies and a subordination of means to ends, it follows that there must be working in and through all nature a directive principle, a principle of plan or design, a principle according to which those manifold agencies work together in fulfilment of a [pg 362] purpose, for the attainment of ends. Hence the reality of a fourth class of causes, final causes.
The separate influence of each of those four kinds of cause can be clearly illustrated by reference to the production of any work of art. When, for instance, a sculptor chisels a statue from a block of marble, the latter is the material cause (materia secunda) of the statue, the form which he induces on it by his labour is the formal cause (forma accidentalis), the sculptor himself as agent is the efficient cause, and the motive from which he works—money fame, esthetic pleasure, etc.—is the final cause.
The formal and material causes are intrinsic to the effect; they constitute the effect in facto esse, the distinction of each from the latter being an inadequate real distinction. It is not so usual nowadays to call these intrinsic constitutive principles of things causes of the latter; but they verify the general definition of cause. The other two causes, the efficient and the final, are extrinsic to the effect, and really and adequately distinct from it,[442] extrinsic principles of its production, its fieri.
This classification of causes is adequate;[443] it answers all the questions that can be asked in explanation of the production of any effect: a quo? ex quo? per quid? propter quid? Nor is there any sort of cause which cannot be brought under some one or other of those four heads. What is called an “exemplar cause,” causa exemplaris, i.e. the ideal or model or plan in the mind of an intelligent agent, according to which he aims and strives to execute his work, may be regarded as an extrinsic formal cause; or again, in so far as it aids and equips the agent for his task, an efficient cause; or, again, in so far as it represents a good to be realized, a final cause.[444]
The objects of our knowledge are in a true sense causes of our knowledge: any such object may be regarded as an efficient cause, both physical and moral, of this knowledge, in so far as by its action on our minds it determines the activity of our cognitive faculties; or, again, as a final cause, inasmuch as it is the end and aim of the knowledge.
The essence of the soul is, as we have seen ([69]), not exactly an efficient cause of the faculties which are its properties; but it is their final cause, inasmuch as their raison d'être is to perfect it; and their subjective or material cause, inasmuch as it is the seat and support of these faculties.