The logical presuppositions of Spinoza's philosophy lie in the fundamental ideas of Descartes, which Spinoza accentuates, transforms, and adopts. Three pairs of thoughts captivate him and incite him to think them through: first, the rationalistic belief in the power of the human spirit to possess itself of the truth by pure thought, together with confidence in the omnipotence of the mathematical method; second, the concept of substance, together with the dualism of extension and thought; finally, the fundamental mechanical position, together with the impossibility of interaction between matter and spirit, held in common with the occasionalists, but reached independently of them. Whatever new elements are added (e. g., the transformation of the Deity from a mere aid to knowledge into its most important, nay, its only object; as, also, the enthusiastic, directly mystical devotion to the all-embracing world-ground) are of an essentially emotional nature, and to be referred less to historical influences than to the individuality of the thinker. The divergences from his predecessors, however, especially the extension of mechanism to mental phenomena and the denial of the freedom of the will, inseparable from this, result simply from the more consistent application of Cartesian principles. Spinoza is not an inventive, impulsive spirit, like Descartes and Leibnitz, but a systematic one; his strength does not lie in brilliant inspirations, but in the power of resolutely thinking a thing through; not in flashes of thought, but in strictly closed circles of thought. He develops, but with genius, and to the end. Nevertheless this consecutiveness of Spinoza, the praises of which have been unceasingly sung by generations since his day, has its limits. It holds for the unwavering development of certain principles derived from Descartes, but not with equal strictness for the inter-connection of the several lines of thought followed out separately. His very custom of developing a principle straight on to its ultimate consequences, without regard to the needs of the heart or to logical demands from other directions, make it impossible for the results of the various lines of thought to be themselves in harmony; his vertical consistency prevents horizontal consistency. If the original tendencies come into conflict (the consciously held theoretical principles into conflict with one another, or with hidden aesthetic or moral principles), either one gains the victory over the other or both insist on their claims; thus we have inconsistencies in the one case, and contradictions in the other (examples of which have been shown by Volkelt in his maiden work, Pantheismus und Individualismus im Systeme Spinozas, 1872). Science demands unified comprehension of the given, and seeks the smallest number of principles possible; but her concepts prove too narrow vessels for the rich plenitude of reality. He who asks from philosophy more than mere special inquiries finds himself confronted by two possibilities: first, starting from one standpoint, or a few such, he may follow a direct course without looking to right or left, at the risk that in his thought-calculus great spheres of life will be wholly left out of view, or, at least, will not receive due consideration; or, second, beginning from many points of departure and ascending along converging lines, he may seek a unifying conclusion. In Spinoza we possess the most brilliant example of the former one-sided, logically consecutive power of (also, no doubt, violence in) thought, while Leibnitz furnishes the type of the many-sided, harmonistic thinking. The fact that even the rigorous Spinoza is not infrequently forced out of the strict line of consistency, proves that the man was more many-sided than the thinker would have allowed himself to be.
To begin with the formal side of Spinozism: the rationalism of Descartes is heightened by Spinoza into the imposing confidence that absolutely everything is cognizable by the reason, that the intellect is able by its pure concepts and intuitions entirely to exhaust the multiform world of reality, to follow it with its light into its last refuge.[1] Spinoza is just as much in earnest in regard to the typical character of mathematics. Descartes (with the exception of an example asked for in the second of the Objections, and given as an appendix to the Meditations, in which he endeavors to demonstrate the existence of God and the distinction of body and spirit on the synthetic Euclidean method), had availed himself of the analytic form of presentation, on the ground that, though less cogent, it is more suited for instruction since it shows the way by which the matter has been discovered. Spinoza, on the other hand, rigorously carried out the geometrical method, even in externals. He begins with definitions, adds to these axioms (or postulates), follows with propositions or theorems as the chief thing, finally with demonstrations or proofs, which derive the later propositions from the earlier, and these in turn from the self-evident axioms. To these four principal parts are further added as less essential, deductions or corollaries immediately resulting from the theorems, and the more detailed expositions of the demonstrations or scholia. Besides these, some longer discussions are given in the form of remarks, introductions, and appendices.
[Footnote 1: Heussler's objections (Der Rationalismus des 17 Jahrhunderts, 1885, pp. 82-85) to this characterization of Kuno Fischer's are not convincing. The question is not so much about a principle demonstrable by definite citations as about an unconscious motive in Spinoza's thinking. Fischer's views on this point seem to us correct. Spinoza's mode of thinking is, in fact, saturated with this strong confidence in the omnipotence of the reason and the rational constitution of true reality.]
If everything is to be cognizable through mathematics, then everything must take place necessarily; even the thoughts, resolutions, and actions of man cannot be free in the sense that they might have happened otherwise. Thus there is an evident methodological motive at work for the extension of mechanism to all becoming, even spiritual becoming. But there are metaphysical reasons also. Descartes had naïvely solved the anthropological problem by the answer that the interaction of mind and body is incomprehensible but actual. The occasionalists had hesitatingly questioned these conclusions a little, the incomprehensibility as well as the actuality, only at last to leave them intact. For the explanation that there is a real influence of body on mind and vice versa, though not an immediate but an occasional one, one mediated by the divine will, is scarcely more than a confession that the matter is inexplicable. Spinoza, who admits neither the incognizability of anything real, nor any supernatural interferences, roundly denies both. There is no intercourse between body and soul; yet that which is erroneously considered such is both actually present and explicable. The assumed interaction is as unnecessary as it is impossible. Body and soul do not need to act on one another, because they are not two in kind at all, but constitute one being which may be looked at from two different sides. This is called body when considered under its attribute of extension, and spirit when considered under its attribute of thought. It is quite impossible for two substances to affect each other, because by their reciprocal influence, nay, by their very duality, they would lose their independence, and, with this, their substantiality. There is no plurality of substances, but only one, the infinite, the divine substance. Here we reach the center of the system. There is but one becoming and but one independent, substantial being. Material and spiritual becoming form merely the two sides of one and the same necessary world-process; particular extended beings and particular thinking beings are nothing but the changeable and transitory states (modi) of the enduring, eternal, unified world-ground. "Necessity in becoming and unity of being," mechanism and pantheism—these are the controlling conceptions in Spinoza's doctrine. Multiplicity, the self-dependence of particular things, free choice, ends, development, all this is illusion and error.
%(a) Substance, Attributes, and Modes%.—There is but one substance, and this is infinite (I. prop. 10, schol; prop. 14, cor. 1). Why, then, only one and why infinite? With Spinoza as with Descartes independence is the essence of substantiality. This is expressed in the third definition: "By substance I understand that which is in itself and is conceived by means of itself, i.e., that the conception of which can be formed without the aid of the conception of any other thing." Per substantiam intelligo id, quod in se est et per se concipitur; hoc est id, cujus conceptus non indiget conceptu alterius rei, a quo formari debeat. An absolutely self-dependent being can neither be limited (since, in respect to its limits, it would be dependent on the limiting being), nor occur more than once in the world. Infinity follows from its self-dependence, and its uniqueness from its infinity.
Substance is the being which is dependent on nothing and on which everything depends; which, itself uncaused, effects all else; which presupposes nothing, but itself constitutes the presupposition of all that is: it is pure being, primal being, the cause of itself and of all. Thus in Spinoza the being which is without presuppositions is brought into the most intimate relation with the fullness of multiform existence, not coldly and abstractly exalted above it, as by the ancient Eleatics. Substance is the being in (not above) things, that in them which constitutes their reality, which supports and produces them. As the cause of all things Spinoza calls it God, although he is conscious that he understands by the term something quite different from the Christians. God does not mean for him a transcendent, personal spirit, but only the ens absolute infinitum (def. sexta), the essential heart of things: Deus sive substantia.
How do things proceed from God? Neither by creation nor by emanation. He does not put them forth from himself, they do not tear themselves free from him, but they follow out of the necessary nature of God, as it follows from the nature of the triangle that the sum of its angles is equal to two right angles (I. prop. 17, schol.). They do not come out from him, but remain in him; just this fact that they are in another, in God, constitutes their lack of self-dependence (I. prop. 18, dem.: nulla res, quae extra Deum in se sit). God is their inner, indwelling cause (causa immanens, non vero transiens.—I. prop. 18), is not a transcendent creator, but natura naturans, over against the sum of finite beings, natura naturata (I. prop. 29, schol.): Deus sive natura.
Since nothing exists out of God, his actions do not follow from external necessity, are not constrained, but he is free cause, free in the sense that he does nothing except that toward which his own nature impels him, that he acts in accordance with the laws of his being (def. septima: ea res libera dicitur, quae ex sola suae naturae necessitate existit et a se sola ad agendum determinatur; Epist. 26). This inner necessitation is so little a defect that its direct opposite, undetermined choice and inconstancy, must rather be excluded from God as an imperfection. Freedom and (inner) necessity are identical; and antithetical, on the one side, to undetermined choice and, on the other, to (external) compulsion. Action in view of ends must also be denied of the infinite; to think of God as acting in order to the good is to make him dependent on something external to him (an aim) and lacking in that which is to be attained by the action. With God the ground of his action is the same as the ground of his existence; God's power and his essence coincide (I. prop. 34: Dei potentia est ipsa ipsius essentia). He is the cause of himself (def. prima: per causam sui intelligo id, cujus essentia involvit existentiam, sive id, cujus natura non potest concipi nisi existens); it would be a contradiction to hold that being was not, that God, or substance, did not exist; he cannot be thought otherwise than as existing; his concept includes his existence. To be self-caused means to exist necessarily (I. prop. 7). The same thing is denoted by the predicate eternal, which, according to the eighth definition, denotes "existence itself, in so far as it is conceived to follow necessarily from the mere definition of the eternal thing."
The infinite substance stands related to finite, individual things, not only as the independent to the dependent, as the cause to the caused, as the one to the many, and the whole to the parts, but also as the universal to the particular, the indeterminate to the determinate. From infinite being as pure affirmation (I. prop. 8, schol. I: absoluta affirmatio) everything which contains a limitation or negation, and this includes every particular determination, must be kept at a distance: determinatio negatio est (Epist. 50 and 41: a determination denotes nothing positive, but a deprivation, a lack of existence; relates not to the being but to the non-being of the thing). A determination states that which distinguishes one thing from another, hence what it is not, expresses a limitation of it. Consequently God, who is free from every negation and limitation, is to be conceived as the absolutely indeterminate. The results thus far reached run: Substantia una infinita—Deus sive natura—causa sui (aeterna) et rerum (immanens)—libera necessitas—non determinata. Or more briefly: Substance = God = nature. The equation of God and substance had been announced by Descartes, but not adhered to, while Bruno had approached the equation of God and nature—Spinoza decisively completes both and combines them.
A further remark may be added concerning the relation of God and the world. In calling the infinite at once the permanent essence of things and their producing cause, Spinoza raises a demand which it is not easy to fulfill, the demand to think the existence of things in substance as a following from substance, and their procession from God as a remaining in him. He refers us to mathematics: the things which make up the world are related to God as the properties of a geometrical figure to its concepts, as theorems to the axiom, as the deduction to the principle, which from eternity contains all that follows from it and retains this even while putting it forth. It cannot be doubted that such a view of causality contains error,—it has been characterized as a confusion of ratio and causa, of logical ground and real cause,—but it is just as certain that Spinoza committed it. He not only compares the dependence of the effect on its cause to the dependence of a derivative principle on that from which it is derived, but fully equates the two; he thinks that in logico-mathematical "consequences" he has grasped the essence of real "effects": for him the type of all legality, as also of real becoming, was the necessity which governs the sequence of mathematical truths, and which, on the one hand, is even and still, needing no special exertion of volitional energy, while, on the other, it is rigid and unyielding, exalted above all choice. Philosophy had sought the assistance of mathematics because of the clearness and certainty which distinguish the conclusions of the latter, and which she wished to obtain for her own. In excess of zeal she was not content with striving after this ideal of indefectible certitude, but, forgetting the diversity of the two fields, strove to imitate other qualities which are not transferable; instead of learning from mathematics she became subservient to it.