The way in which Spinoza arrived at his main conceptions is rather obscured by the geometric method of exposition pursued in his Ethics. Briefly it was this. To understand any finite object or event it is necessary to follow up innumerable conditions on which it depends. These ramify in all directions, yet we can never halt, for the conditions invoked are themselves dependent on innumerable others. But a world consisting entirely of depend ent objects and events would be unintelligible, inconceivable. There must be some unconditioned, self-dependent, absolute reality, or Substance, to account for the reality of all that is con ditioned and dependent. This is usually admitted. But the tra ditional solution, accepted by Descartes and the greatest scientists of the 17th century, was that God, a supernatural omnipotent Being, is this self-existent, absolute Being or Substance, who has created all things and maintains them. But the idea of an external Creator did not satisfy Spinoza. His rationalism revolted against the arbitrariness implied in the creation having taken place at one time rather than another; nor could it find in the notion of creation out of nothing anything more intelligible than the prob lems it was intended to solve. If it is necessary to posit an absolute ground of reality, why not accept the system of reality itself as this self-dependent substance? This view avoided the unnecessary multiplication of entities, and the difficulties of creation out of nothing. It was also more satisfactory to the religious side of Spinoza's character, for it brought man into more intimate relation with God. Such a view was, of course, only possible in consequence of the friendlier attitude towards Nature which the Renaissance cultivated, as against the hostile association of "the world, the flesh and the devil" characteristic of mediaeval Christianity. With regard to the structure of the cosmic system, the leading ideas of Spinoza may be summarized as follows. God (or Nature or Substance) is not static but dynamic, and exercises all the kinds of energy that there are. It alone is absolutely infinite or absolutely perfect. Each kind of energy that is ultimate, that is, irreducible to any other kind, Spinoza calls an attribute of substance. Spinoza refers to an infinity of such attributes. But by "infinite" he means "complete" (not innumerable) and by "finite" incomplete or fragmentary. Man only knows two such attributes, namely ex tension and thought, that is, physical energy and mind energy. There may be others ; there probably are. Moreover, each attri bute is infinite of its kind, that is, exhausts everything of its own kind, so that there is no physical energy outside extension, nor mind energy outside thought.
All finite bodies and physical events are "modes," that is, modi fications or states, of extension, and all minds and mental ex periences are modes of thought. Similarly with the other attri butes, if any. All cosmic activities or processes are immanent, not transcendent. And all apparent interactions between the modes of different attributes, say that between the body and soul of man, result from the fact that they are concomitant expressions of the attributes of the one substance. "The order and connection of thoughts is the same as the order and connection of things." Physical effects should be traced to physical causes, and mental experiences to mental causes. The various finite modes come into being. and pass away; but not into nothingness—for the One remains in which the many change. God as conceived by Spinoza is not a "personal" God, not however because He is less, but because He is infinitely more than any personality known to man. (See SPINOZA; PANTHEISM ; ETHICS, HISTORY OF; KNOWLEDGE, THEORY OF.) Leibniz (1646-1716) was influenced mainly by his faith in the permanent reality of individual souls. His philosophy, accord
ingly, is so constructed as to secure the ultimate reality of in dividuals, and to assure their permanence. To this end two things were felt to be necessary. He had to dissociate souls from physical atoms, and to treat each individual soul as a kind of "substance," or self-contained thing. The Cartesian identification of matter with extension (which was widely accepted then) prompted Leibniz to deny the reality of matter altogether. For matter is then infinitely divisible, and no real "atom," nothing ultimate and really indivisible, can be conceived for the con struction of the composite bodies of ordinary observation. From this he concluded that all space or all material bodies are mere subjective appearances, not objective realities. Reality, accord ing to Leibniz, consists entirely of souls or spirits of all degrees of development. These are the real "atoms" or "individuals," real unities not made up of parts. Some of them have only a very low degree of consciousness or sub-consciousness, they are in a state of chronic somnolence, so to say; some are in something like a dream state; others are more awake, have clear thoughts, or are even self-conscious; and God, the "monad of monads" is supremely conscious and active. There is an infinity of monads; their gradation is continuous, without a break; and no two are exactly alike.
To avoid the tendency to pantheism, Leibniz regarded the monads as not interconnected in any way, as incapable of in fluencing one another—"they have no windows by which anything can come in or go out." But there is one important exception to this, for God has created all other monads, which are "emana tions" from the monad of monads. This, of course, makes the supreme monad different in kind, not merely different in degree from the other monads. However, having conceived the monads as "without windows" Leibniz has now to explain the appearance of interaction between them—the apparent interaction, e.g., between the assembly of less developed monads which look like a body and that higher monad which is the soul. The problem is very like the problem which confronted the Cartesians, and the solution offered by Leibniz is rather like occasionalism. The ordinary monads do not really interact ; each is self-contained, and develops from within, its present being pregnant with its future. But God has so made them all that they act in harmony. It is as if He had wound up so many clocks to keep time together. There is thus a "pre-established harmony" in consequence of which also each monad may be regarded as mirroring the entire universe, or every other monad, from its own point of view.
Like Descartes, Leibniz also follows strictly mechanical methods in dealing with physical problems, but he conceives mechanism to be in the service of teleology, and his general outlook, of course, was essentially teleological. His conception of the relation be tween the supreme monad and the other monads is obviously supernatural. In his philosophy, as in his public activities, Leib niz tried to bring together too many different elements to succeed in unifying them in one system. Leibniz is also famous for his optimism, that is, for holding the view that the actual world is "the best of all possible worlds." What he meant was that the "pre-established harmony" actually established by God was chosen by Him as the best possible, out of an endless variety of possibilities, in view of the purpose which He had in view. This does not imply that each thing regarded by itself is the best of its kind, or even good. It means only that in order to make any one thing better, the entire scheme of things would have to be different, and, as a whole, rather worse. (See LEIBNIZ ; IDEALISM; KNOWLEDGE, THEORY OF ; OPTIMISM.)