The Principle of Sufficient Reason: A Thomist Critique?

A Study

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I. Introduction

In the twentieth century, and especially in its latter half, it became fashionable for Catholic philosophers to critique the Principle of Sufficient Reason (PSR), first set down in explicit form by Leibniz and erected into a demonstrated axiom by Wolff. Simply put, this principle states that there is nothing that is without a sufficient reason. Leibniz and Wolff attached various corollaries to this principle (the interpretation of which is constantly disputed by historians of philosophy, who would be out of a job otherwise), but these corollaries stand outside the principle in its bare form.

According to these Catholic critics, there was a radical shift in Catholic philosophy (and, therefore, theology) with the wide acceptance of this principle — a shift which, in their telling, culminated in many of the intellectual vices of the first half of the twentieth century.

I am neither a philosopher nor a historian of philosophy, yet I am a Thomist who attempts to conform my mind as much as possible to the judgements of the classical authorities of the Thomistic school. Therefore, I believe that it is important for myself and others who hold the same praxis to consider carefully how the Thomists actually interacted with the PSR, and how they justified using language which was novel to philosophy.

In this, what we will see is that, while accepting the principle itself as both true AND traditional (although not in that form of words), they critiqued the use of the principle and the corollaries drawn from it by Leibniz and Wolff. We can leave it to the historians of philosophy to tell us whether these Thomists properly understood Leibniz and Wolff in their corollaries. This does not concern us here.

II. The Two Senses of the Principle

The fact that our acceptance of the Leibnizian invention is to be limited is quite clear in a number of different Thomists. Zigliara states that “this Leibnizian opinion, kept within due limits, ought to be admitted, and, rather than an opinion, it is to be called a proposition per se nota.” (Ontologia, lib. IV, cap. I, art. II) Hugon adds the restriction “as it is accepted by the Scholastics” and “taken in the scholastic sense.” (Metaphysica ontologica, tract. IV, q. I, art. IV) Sanseverino states that Leibniz “exalted [this principle] beyond measure.” (Ontologia, cap. II, art. IV)

Still other authors, while explaining the matter in the same way as the rest of the school, will flatly say that Leibniz’s principle was false — not insofar as the principle of sufficient reason itself is false (which they affirm, prove, and apply), but insofar as Leibniz gave some determination in the treatment of this matter. As an example, Mancini (who will be quoted below) calls the principle of sufficient reason “a doctrine altogether false” in the “Leibnizian sense,” while in the midst of a lengthy treatment explaining the exact sense in which the principle of sufficient reason is true — a principle which appears throughout his works, where he makes use of it (Critica, q. VII, art. 3).

This is something important to remember, so that one does not err in reading the Thomists on this matter. Two things are true and must be kept in mind:

a) The principle of sufficient reason was rejected in the Leibnizian sense (although, occasionally, this is simply referred to as the “principle of sufficient reason,” leading to some confusion). This is the principle with certain definitions and corollaries that were posited by Leibniz and Wolff.

b) The principle of sufficient reason was accepted in the Scholastic sense, which, according to many authors, is truly a principle that “Leibniz took from the ancients” (Sanseverino, Elementa, vol. II, § 63), which they argue has always been present in a more general or less distinct form in Aristotle and the Scholastics, along with philosophers of many schools in their own determinations.

III. Sufficient Reason, Principle, and Cause

For the definition of this principle, the authors begin by distinguishing three terms: cause, principle, and sufficient reason. While these three terms are distinct from one another, they are related as species to genus. For the cause is a type of principle, yet there are principles that are not causes; similarly, the principle is a type of sufficient reason, yet there are sufficient reasons that are not principles. Buonpensiere gives a good treatment of these three concepts:

A sufficient reason is everything that logically explains a fact of agreement or disagreement among various elements or notions... the elements or notions between which some sufficient reason is established are not always really distinct, but are sometimes distinct only by reason; as is plain in the case of God’s immutability and eternity.

A principle is that from which something else... proceeds, in whatever way it may proceed... the elements or things between which the character of principle and of principiatum is found are always really distinct from one another. Nevertheless the principiatum does not always express a relation of dependence upon its principle...

A cause is a principle physically infusing being into something other than itself, which is called the effect... between cause and effect there is not only always a real distinction... there is also always found a true and real dependence of the effect upon its own cause. (Commentaria in Iam Partem Summae Theologicae, q. IV, art. III)

The relationship between these three concepts should be easy to understand. The principle adds to the concept of sufficient reason the real distinction between the two terms; the cause adds to the concept of principle the real dependence of the one term on the other term. From this, we can see more clearly the real state of the question that we are asking with the affirmation of the principle of sufficient reason.

IV. What the Principle Affirms — and What It Does Not

This principle is called “sufficient” insofar as nothing beyond what is posited is demanded in order to constitute it as such. Any attempt to make the “sufficient reason” necessitating is rejected by the Thomists, since this would be false in many cases — e.g., free will, divine liberty, etc.

“Sufficient reason” in the Leibnizian sense is a doctrine altogether false. For he understands under “sufficient reason” a certain necessary and ineluctable determination, in all causes, toward producing determinate effects. And this notion, if it be taken universally, destroys from the foundations the very nature of liberty: both in God, since he would do all things by necessity, and in creatures, since liberty, as we shall see in Metaphysics, necessarily requires indifference both on the side of the subject and on the side of the object. (Mancini, Critica, q. VII, art. 3)

Thomists commonly give a distinction between three aspects in which we accept the principle of sufficient reason: “the reason of the thing in essence, the reason of the thing in existence, the reason of the thing in knowability.” (Hugon, Metaphysica ontologica, tract. IV, q. I, art. IV)

a) In the first case, nothing beyond the reason is demanded in order to constitute the thing in its essence;

b) In the second case, nothing beyond the reason is demanded in order to constitute the thing in its existence;

c) In the third case, nothing beyond the reason is demanded in order to constitute something as knowable.

When we ask “whether the principle of sufficient reason is universal,” we are not asking whether all things whatsoever have causes or principles; nor are we asking whether all things whatsoever are necessitated by some reason; rather, we are asking whether, in order for something to exist, there needs to be some reason sufficient to explain why it exists rather than does not exist. Any other corollary drawn by Leibniz or Wolff can be denied without rejecting the principle itself.

V. The Proof of the Principle

The proof of this principle of sufficient reason is relatively simple. It must be noted that the principle of sufficient reason is an immediate analytic judgement, something that is per se nota — Gredt (Elementa philosophiae, vol. II, thesis XXIII) says it is “per se notum omnibus,” self-evident to all, and Zigliara that it is “rather than an opinion... a proposition per se nota.” (Ontologia, lib. IV, cap. I, art. II) It follows from this that the principle of sufficient reason cannot be demonstrated a priori in the proper sense, but can only be vindicated by a reduction to the principle of non-contradiction, by an analysis of the terms, or by a reductio ad absurdum.

Zigliara proves it thus: “in order that something exist, and exist in this way or in that, there is required something by which it is determined both as to its existing and as to its mode of existing, whether that something lie in the nature of the existing thing or in the cause from which the thing exists.” (Ontologia, lib. IV, cap. I, art. II) Gredt says something similar: “the sufficient reason is that whereby something is what it is... that whereby it is sufficiently determined to be what it is... But whatever is, whether existent or merely possible, has at least in itself and through itself that whereby it is what it is.” (Elementa philosophiae, vol. II, thesis XXIII) Hugon gives a fuller proof:

The sufficient reason is that which being given, the thing is determined in its quiddity, or existence, or intelligibility. Now nothing can be without that by which it is determined in essence, existence, or intelligibility; for an indeterminate essence is nothing in the order of essence, nor an indeterminate existence in the order of existence, nor an indeterminate intelligibility in the order of intelligibility. Therefore nothing can be without a sufficient reason....

Common sense evidently pronounces that a thing which does not have what suffices for being, in fact is not; that a thing which does not have what suffices for its being understood, in fact is not understood. If there is no reason by which the being of a thing is distinguished from non-being, or by which intelligibility is distinguished from non-intelligibility, then the thing will with equal right be called non-being, or non-intelligible. Therefore whatever is (whether under the aspect of quiddity, or of existence, or of intelligibility) has a sufficient reason. (Metaphysica ontologica, tract. IV, q. I, art. IV)

Sanseverino gave two other arguments from the fact of God’s creation of the world:

First, it is certain that God did not found this world without some reason. For, since the creation of the world is not a necessary but a free work of God, there had to be something through which God determined himself to create the world. But that through which God determined himself to create the world is the sufficient reason on account of which the world exists. Therefore the world does not exist without a sufficient reason. Secondly, it is also certain that all the things of which the world is compounded are connected among themselves; otherwise the unity of the world could not have been effected by them. Now this connection of mundane things shows that God did not give to the individual natures of things their definite modes of existing without particular reasons, since to effect that connection it is required that each and every nature have that mode of existing which answers to the place it occupies and to the offices it must discharge in the world. But that by which a thing is determined to existing in a definite way is the sufficient reason why it exists. Therefore, besides the sufficient reason of the existence of the world, there must be sufficient reasons of the existence of the individual things of which the world consists. Wherefore it is to be held as certain that nothing exists without some sufficient reason. (Elementa, vol. II, § 63)

These arguments are repeated by many scholastic philosophers.

VI. Universal in the Strict Sense: God and Creatures, Necessary and Contingent

From these arguments, Zigliara and others draw, as a corollary, the perfection of the principle of sufficient reason. While the principle of causality has a limitation to things that exist from another (i.e., effects), the principle of sufficient reason is something that applies to all things, both created and uncreated, temporal and eternal, God and creature. Therefore, the restriction that is offered by Leibniz and others of this principle to merely contingent things is false. From this, it follows that all things, both necessary and contingent, can be resolved into a sufficient reason (even while this may not appear to us).

Ironically, one of the points for which the Thomists critiqued the Leibnizians was precisely their restriction of the principle of sufficient reason to contingent truths alone. The scholastics held that the principle of sufficient reason held not only for contingent and necessary being, but even for intentional and possible being as well. Equally ironic (as Kleutgen points out) is the fact that if we were to state the principle of sufficient reason for contingents only, then we would be merely stating the principle of causality — which is obviously present in the Scholastics in a much clearer form: “with this restriction, it says only what the ancients expressed, if not with more exactness, at least with more clarity, by the well-known axiom: Non est effectus sine causa.” (Die Philosophie der Vorzeit vertheidigt, n. 292) The Thomists held that the principle of sufficient reason applied to all truths, both contingent and necessary:

Leibniz narrowed the principle of sufficient reason to contingent truths. Upon two great principles, according to him, our reasonings are built: the first, for necessary truths, is the principle of contradiction, in virtue of which the essential predicates belong to a thing; the other, for contingent truths, is the principle of sufficient reason, in virtue of which predicates outside the essence belong to a thing. (Hugon, Metaphysica ontologica, tract. IV, q. I, art. IV)

VII. Sufficient Reason and Causality Are Not the Same Principle

Commonly, texts from St. Thomas (e.g., Summa contra Gentiles I, cc. 86–87) will be cited in favor of this extension, where the Angelic Doctor distinguishes, in God’s willing of creatures, between God’s will having a cause (which it does not have) and God’s will having a reason (which it does have). From this, they critique those who would collapse and identify the principle of causality and the principle of sufficient reason into a single principle. Further, they also cite the distinction given by the scholastics when treating the demonstration propter quid, where the scholastics deny that a true and proper cause is required for a demonstration propter quid: it is sufficient to give the reason of the thing. It is in this latter way that Kleutgen and others argue for the antiquity of the principle of sufficient reason.

While some attempted to identify the principle of sufficient reason and the principle of causality, this is rejected by the Thomists. This is clear from what was said above. A cause implies real distinction and real dependence between the principle and the effect. Yet not everything that exists verifies this (e.g., the divine processions concern the persons as principle without being cause, due to the lack of real dependence). Therefore, while the principle of sufficient reason is universal and applies to all things, the principle of causality has a restricted acceptation. Further, while the principle of causality is true of a thing in its becoming (since cause regards such a state), which is restricted, the principle of sufficient reason is true of a thing in its being, which is universal.

The principle of sufficient reason extends to every being, and touches essence, existence, intelligibility; the principle of causality, however, regards not every being, but contingent existence. Wherefore every cause is a sufficient reason, but not every sufficient reason is a cause. The difference between the two principles appears from the manner in which each is expressed. In the principle of sufficient reason the subject (everything that is) extends more widely than in the principle of causality (everything that comes to be or begins); the predicate, to have a reason, is likewise wider than to have a cause. God is to Himself His sufficient reason, but He is not to Himself a cause. (Hugon, Metaphysica ontologica, tract. IV, q. I, art. IV)

For this reason, if “sufficient reason” were meant to indicate something really distinct from that of which it is the sufficient reason, then the principle would be manifestly false (e.g., in the case of the sufficient reason of the Divine attributes). Therefore, Gredt distinguishes between two kinds of sufficient reason: the intrinsic sufficient reason and the extrinsic sufficient reason: “there is an intrinsic sufficient reason, of being (essendi), and an extrinsic sufficient reason, of becoming (fiendi). A cause is an extrinsic sufficient reason, of becoming, really distinct from the effect.” (Elementa philosophiae, vol. II, thesis XXIII) When we consider something in its becoming, there is an extrinsic sufficient reason (i.e., the cause; cf. Garrigou-Lagrange, God: His Existence and His Nature, n. 24), which allows us to apply the principle of causality to all things that become. When we consider something in its being, there is either an intrinsic sufficient reason or an extrinsic sufficient reason; therefore, the principle can apply to all things that are, including God.

The principle contains both of these kinds of sufficient reason in a confused manner, allowing for its universality. In order to understand the principle in its full force, we can use the formulation of Fr. Garrigou-Lagrange: “Every being has a sufficient reason, either in itself or in some other being, for being what it is; in itself, if what constitutes it as such belongs to it by its very nature; in another, if what is attributed to it does not belong to it by its very nature.” (God: His Existence and His Nature, n. 24)

VIII. The Principle and the Free Will

On another point, the scholastics critique those who would wrongly apply the principle of sufficient reason to the will. The will, in order to be free, has objective indifference to a multiplicity of goods set before it, and not merely the freedom from coaction that certain heretics tried to apply to the will. Therefore, if we were to apply the principle of sufficient reason to the objective order (as if the goodness of the object itself were a necessitating reason explaining how the will acted in such and such a way), then we would be in error; for, while the goodness of the object is sufficient to explain the motion of the will in the objective line, since the will has objective indifference to finite goods, such goodness is not necessitating. Yet, as long as we reject this — holding that the sufficient reason for the motion of the will towards its object is found in the choice of the will in the efficient line, and in a non-necessitating manner in the objective line — then we hold to the truth of the matter and the truth of the principle:

If the principle of sufficient reason is taken objectively, in relation to the free will, it does not possess truth; and on this side the doctrine of Leibniz is immoderate and false. For the reason by which the free will determines itself to the exercise of its act is not the object, but its own choice, elicited by the will itself. Hence whenever the will chooses, there is indeed some sufficient reason, both objective and subjective; but this sufficient reason, objectively considered, is not a principle necessarily determinative of the will’s election. (Zigliara, Ontologia, lib. IV, cap. I, art. II)

Mattiussi puts the same resolution in a formula: “What is lacking is the sufficient reason of a necessary act, as the determinists would have it... What is not lacking is the sufficient reason of a free act.” For more about this, cf. Mattiussi, Le XXIV tesi della filosofia di S. Tommaso d’Aquino approvate dalla S. Congregazione degli Studi, cap. XII; Garrigou-Lagrange, God: His Existence and His Nature, n. 61, where the relations between free will and the absolutely necessary principles of reason and being are treated at length.

NOTE. I realized upon completing this article that I completely forgot one of the critiques commonly given by Thomists against the Leibnizian articulation of the PSR. They accused Leibniz and Wolff of making the sufficient reason into a necessitating reason, which overthrew the order of truly free and contingent causes. This is related to this section on the freedom of the will and was often treated in conjunction with refutations of their optimism.

IX. Not the Absolutely First Principle

As Hugon indicates in the passage quoted in section VI, Leibniz’s invocation of the principle was to set up two first principles: one for necessary things (the principle of non-contradiction) and another for contingent things (the principle of sufficient reason). This leads us to the next point of critique by the Thomists. They rejected that the principle of sufficient reason could be called the absolutely first principle in any line, whether of necessary things or of contingent things. The principle of sufficient reason itself resolves into the principle of non-contradiction, which precludes it from being the absolutely first principle in any sense.

Leibniz said that, just as the principle of contradiction is the first principle of human knowledge with respect to purely necessary truths, so it was necessary to admit for contingent truths another first principle, granting this prerogative to the principle called of sufficient reason, which is usually expressed by this formula: nothing exists without a sufficient reason. From this he inferred that experimental propositions known by induction, and synthetic judgments into which the element of experience enters, rest upon the principle of sufficient reason, in the same way that analytic judgments... recognize as their basis the principle of contradiction. This assertion of Leibniz is absolutely untenable at bottom, and contains at the very least much inaccuracy and confusion of ideas. (González, Estudios sobre la filosofía de Santo Tomás, cap. X)

As noted by González, Mancini, and others, the Leibnizian error here seems to stem from a basic confusion. First, when we speak of synthetic judgements, we can refer either to particular facts (e.g., “I write”) or to universal judgements (e.g., “every planet receives its light from the sun”). In the former case, it is obviously absurd even to pretend that the principle of sufficient reason is a necessary presupposition for this sort of knowledge. Rather, such particular synthetic judgements are directly resolved into experience.

In the latter case, it is clearly the fact that such judgements do presuppose some affirmation of the principle of sufficient reason, so as to universalize what is simply known by induction. Otherwise, induction would always proceed fallaciously, insofar as the judgement would be nobler than the evidence (a universal judgement coming from the mere enumeration of particulars). Yet, with the influence of a universal analytic judgement, we are able to draw forth a universal judgement from induction:

Since the universality of a judgment cannot be procured by the mere enumeration of cases (for this is always particular and confined to determinate individuals), we must say that an analytic principle comes to its aid — a principle which, including absolute universality, communicates universality to certain experimental judgments that have been extended by observation. And that recourse must be had to this is quite evident. For if the effect cannot exceed the cause, the universality of a judgment can never proceed from singulars, but must proceed from something universal; and what is universal of itself can only be some analytic judgment. (Liberatore, Metaphysica generalis, cap. IV, art. I)

If we speak not of contingent truths generally, but of those which are raised to universality by induction, we freely confess that in a certain sense they do rest, at least indirectly, on the principle of sufficient reason. (ibid., art. II)

Yet there is a problem here. To be an absolutely first principle, it is not sufficient that something merely depend upon another in some way for knowledge. Therefore, while there is some truth to this matter (the principle of sufficient reason is of prime importance in universal synthetic judgements), it is not entirely true (insofar as this does not make the principle a first principle).