SUFFICIENT REASON, PRINCIPLE OF

The principle of sufficient reason states that everything that exists has a sufficient reason for its existence. Originally proposed by G. W. leibniz, it has been incorporated into neoscholastic thought and is commonly listed among the first principles. Opinion is divided as to its proper formulation and ultimate validity.

Leibniz's Formulation. In his systematization of philosophy Leibniz sought a principle that would govern the world of existence or of actual fact just as the principle of contradiction governs the realm of the possible. Such would be a principle "of sufficient reason, in virtue of which we hold that no fact can be genuine or existent and no proposition true unless there is a sufficient reason why it should be so and not otherwise, although for the most part these reasons cannot be known by us" (Monadology 31–32; confer, Principles of Nature and Grace, 7; Theodicy, 1.44).

Thus stated, the principle of sufficient reason has two aspects. As applied to things, it means that everything existent either exists of its nature or has been brought into being by something else that is the reason of its existence. As applied to statements, it means that every true proposition is either a necessary proposition or follows from other true propositions that give the reason of its truth. It is probable that Leibniz regarded all apparently contingent facts and truths as derivatively necessary, for he held that the objects of creation were determined by their belonging to the best possible world, which God was of His nature necessitated to create. If so, the principle of sufficient reason was for Leibniz a principle of universal necessity; he might not have said this explicitly so as not to come into conflict with Christian orthodoxy.

Other Interpretations. Thus understood, Leibniz's principle represents the point of view of systems seeing all reality and history as the unrolling of an intelligible necessity, for example, stoicism, some forms of neoplatonism and the philosophy of spinoza. Equally it looks forward, for example, to Hegelianism. But the principle has also a weaker, but more acceptable meaning in which "sufficient" is distinguished from "determining." In this sense it is compatible with the occurrence of free choice in creatures and with God's freedom to create.

Taken in this way, it is, in its application to contingent things, equivalent to the principle of causality. In its universality it says in effect that everything that exists is either caused or is such as to need no cause. As applied to statements it is equivalent to the principle of intelli gibility. It means that all true statements could ideally commend themselves to the mind by being seen either as necessarily true or as having adequate grounds for being true. This is approximately what scholastics meant by saying that all reality possesses ontological truth (omne ens est verum ). Understood in this way, the principle becomes an acceptable reformulation of something that had always been held in scholastic metaphysics.

Kant and the Principle. C. wolff and A. G. Baumgarten (1714–62) attempted a proof of Leibniz's principle of sufficient reason. In his early Principiorum primorum cognitionis metaphysicae nova dilucidatio (Königsberg 1755), I. kant, while rejecting their proof, tried to offer another. In his critical writings Kant regarded the principle of sufficient reason as the fundamental synthetic a priori proposition, paralleling the principle of contradiction as the fundamental analytic proposition. He states that "the principle of sufficient reason is the basis of possible experience, that is, of the objective knowledge of phenomena, in respect of their relationship in the time-series" (Critique of Pure Reason, A200-1; B246).

In this view, the principle of sufficient reason is valid only within the realm of phenomena as an indispensable means of making them intelligible, and has, in relation to phenomena, a character similar to that attributed to it by Leibniz in relation to real being. As a principle of intelligibility, it means for Leibniz that things are in themselves intelligible and for Kant that we cannot think of things without imposing an intelligible order upon them, which is precisely the general contrast between these two thinkers.

Scholastic Views. Scholastic philosophers usually accept the principle of sufficient reason in the weaker sense described above. They differ, however, about whether its evidence is primary or can in some way be derived from a prior principle and, more generally, about its relationship to other principles.

Some, like R. garrigou-lagrange, hold that the principle of sufficient reason is reducible to the principle of contradiction or the principle of identity. Such authors usually reject the Kantian distinction between analytic and synthetic a priori propositions as misleading, and if willing to use the term analytic at all, describe all self-evident propositions as analytic. They mean in this case that it is impossible in the concrete to contemplate the notion of being adequately without perceiving its radical intelligibility. Being would not be being unless it had all that was needed in order to be, that is, unless it had a sufficient reason for its being. Hence the principle of identity and the principle of sufficient reason are inseparable; the latter is merely an unfolding of what is involved in the former.

Others, like J. Laminne and P. Descoqs, are willing to accept the Kantian distinction of analysis and synthesis, although they regard true synthetic a priori judgments as valid for reality and not only for phenomena in the Kantian sense. On this basis they point out that the notion of reason is not contained in the notion of being and cannot be derived from it. Hence, while the principles of identity and contradiction are analytic, the principle of sufficient reason, introducing in the predicate the notion of reason that is not contained in the subject, is synthetic. It is a self-evident and necessary truth, but its evidence is its own, and it cannot be reduced to any other principle.

These two schools of thought nevertheless have in common that they attribute fundamental importance to the principle of sufficient reason and regard the principle of causality as an application of it to contingent or temporal being. Yet other neoscholastics, like J. Geyser, are less interested in Leibniz's principle and find a primary and independent evidence in the principle of causality.

Critical Evaluation. If the principle of sufficient reason is interpreted as a principle of universal necessity, it is evidently unacceptable in any philosophy that upholds free will in creatures and God's free choice in creation. But, in the wider and looser sense in which it is generally held, its precise logical status is still in need of discussion.

What does one mean when he speaks of the sufficient reason of a thing's existence? There can be no doubt that he usually means its causes. Yet one speaks of God as being the sufficient reason of His own existence. Here it can mean only that His existence, so to say, makes sense without reference to anything other than God. But this is merely to say that God needs no cause; He exists necessarily. What foundation, then, has the distinction between God as the sufficient reason for His own existence and God as existing? In the ontological order, the two are absolutely identical. Hence, when one says that everything that exists has a sufficient reason for its existence, he seems to say that everything that exists is either caused or needs no cause. But this is an empty formal dichotomy. One can, therefore, sympathize with those authors who devote their chief attention to causality, and seek to arrive at principles that offer a criterion of the sort of being that needs to be caused, that is, the contingent, the temporal and the finite.

There is more to be said for Leibniz's formula if it is understood as stating that everything that exists is intelligible. Here one asserts an actual or potential relationship to thought that is applicable even in the case of God. He is saying that, if he understands anything and insofar as he understands anything, he understands how it is that it is so, either because he sees that it is necessarily so or because he finds what has made it so. In principle, however great may be man's ignorance in particular cases, reality responds to the demands of thought. There is harmony between thinking and being. Even so one may judge that this was sufficiently expressed in the older assertion of the ontological truth of things and need not be surprised that the principle of sufficient reason was not formally enunciated by aristotle or St. thomas aqui nas, but was left for Leibniz to formulate.

What modern scholastics have taken the principle of sufficient reason to mean is no doubt true. The question is simply whether its explicit statement adds much or little to what had been stated in other ways before. If an unfavorable view has been suggested here, it must be remembered that other writers have thought otherwise. Difference of opinion is likely to continue.

See Also: first principles; truth; certitude.

Bibliography: j. e. gurr, The Principle of Sufficient Reason in Some Scholastic Systems: 1750–1900 (Milwaukee 1959). d. j. b. hawkins, Being and Becoming (New York 1954). r. garrigoulagrange, God, His Existence and His Nature, tr. b. rose, 2 v. (5th ed. St. Louis 1934–36) 1:181–191. p. descoqs, Institutiones metaphysicae generalis (Paris 1925). a. schopenhauer, On the Fourfold Root of the Principle of Sufficient Reason, and on the Will in Nature, tr. k. hillebrand (rev. ed. London 1907). w. m. urban, History of the Principle of Sufficient Reason: Its Metaphysical and Logical Foundations (Princeton Contributions to Philosophy 1; Princeton 1900) 1–87.

[d. j. b. hawkins]