Structure of reality
According to Spinoza, God has "attributes". One attribute is 'extension', another attribute is 'thought', and there are infinitely many such attributes. Since Spinoza holds that to exist is to act, some readers take 'extension' to refer to an activity characteristic of bodies (for example, the active process of taking up space, exercising physical power, or resisting a change of place or shape). They take 'thought' to refer to the activity that is characteristic of minds, namely thinking, the exercise of mental power. Each attribute has modes. All bodies are modes of extension, and all ideas are modes of thought.
Spinoza's ideas relating to the character and structure of reality are expressed by him in terms of substance, attributes, and modes. These terms are very old and familiar, but not in the sense in which Spinoza employs them. To understand Spinoza, it is necessary to lay aside all preconceptions about them, and follow Spinoza closely. Spinoza found it impossible to understand the finite, dependent, transient objects and events of experience without assuming some reality not dependent on anything else but self-existent, not produced by anything else but eternal, not restricted or limited by anything else but infinite. Such an uncaused, self-sustaining reality he called substance. So, for instance, he could not understand the reality of material objects and physical events without assuming the reality of a self-existing, infinite and eternal physical force which expresses itself in all the movements and changes which occur, as we say, in space.
This physical force he called extension, and described it, at first, as a substance, in the sense just explained. Similarly, he could not understand the various dependent, transient mental experiences with which we are familiar without assuming the reality of a self-existing, infinite and eternal consciousness, mental force, or mind-energy, which expresses itself in all these finite experiences of perceiving and understanding, of feeling and striving. This consciousness or mind-energy he called thought, and described it also, at first, as a substance. Each of these "substances" he regarded as infinite of its kind (that is, as exhaustive of all the events of its own kind), and as irreducible to the other, or any other, substance. But in view of the intimate way in which Extension and Thought express themselves conjointly in the life of man, Spinoza considered it necessary to conceive of Extension and Thought not as detached realities, but as constituting one organic whole or system. And in order to express this idea, he then described Extension and Thought as attributes, reserving the term Substance for the system which they constitute between them. This change of description was not intended to deny that Extension and Thought are substances in the sense of being self-existent, etc. It was only intended to express their coherence in one system. The system of course would be more than any one attribute. For each attribute is only infinite of its kind; the system of all attributes is absolutely infinite, that is, exhausts the whole of reality. Spinoza, accordingly, now restricted the term "substance" to the complete system, though he occasionally continued to use the phrase "substance or attribute", or described Extension as a substance.
As commonly used, especially since the time of Locke, the term substance is contrasted with its attributes or qualities as their substratum or bearer. But this meaning must not be read into Spinoza. For Spinoza, Substance is not the support or bearer of the Attributes, but the system of Attributes — he actually uses the expression "Substance or the Attributes." If there is any difference at all between "Substance" and "the Attributes", as Spinoza uses these terms, it is only the difference between the Attributes conceived as an organic system and the Attributes conceived (but not by Spinoza) as a mere sum of detached forces. Something is still necessary to complete the account of Spinoza's conception of Substance. So far only the two Attributes have been considered, namely, Extension and Thought. Spinoza, however, realised that there may be other Attributes, unknown to man. If so, they are part of the one Substance or cosmic system. And using the term "infinite" in the sense of "complete" or "exhaustive", he ascribed to Substance an infinity of Attributes, that is, all the attributes there are, whether known to man or not.
Now reality, for Spinoza, is activity. Substance is incessantly active, each Attribute exercising its kind of energy in all possible ways. Thus the various objects and events of the material world come into being as modes (modifications or states) of the attribute Extension; and the various minds and mental experiences come into being as modes of the attribute Thought (or Consciousness). These modes are not external creations of the Attributes, but immanent results — they are not "thrown off" by the Attributes, but are states (or modifications) of them, as air-waves are states of the air. Each Attribute, however, expresses itself in its finite modes not immediately (or directly) but mediately (or indirectly), at least in the sense to be explained now. Galilean physics tended to regard the whole world of physical phenomena as the result of differences of motion or momentum. And, though erroneously conceived, the Cartesian conception of a constant quantity of motion in the world led Spinoza to conceive of all physical phenomena as so many varying expressions of that store of motion (or motion and rest).
Spinoza might, of course, have identified Extension with energy of motion. But, with his usual caution, he appears to have suspected that motion may be only one of several types of physical energy. So he described motion simply as a mode of Extension, but as an infinite mode (because complete or exhaustive of all finite modes of motion) and as an immediate mode (as a direct expression of Extension). Again, the physical world (or "the face of the world as a whole", as Spinoza calls it) retains a certain sameness in spite of the innumerable changes in detail that are going on. Accordingly, Spinoza described also the physical world as a whole as an infinite mode of extension ("infinite" because exhaustive of all facts and events that can be reduced to motion), but as a mediate (or indirect) mode, because he regarded it as the outcome of the conservation of motion (itself a mode, though an immediate mode). The physical things and events of ordinary experience are finite modes. In essence each of them is part of the Attribute Extension, which is active in each of them. But the finiteness of each of them is due to the fact that it is restrained or hedged in, so to say, by other finite modes. This limitation or determination is negation in the sense that each finite mode is not the whole attribute Extension; it is not the other finite modes. But each mode is positively real and ultimate as part of the Attribute.
In the same kind of way the Attribute Thought exercises its activity in various mental processes, and in such systems of mental process as are called minds or souls. But in this case, as in the case of Extension, Spinoza conceives of the finite modes of Thought as mediated by infinite modes. The immediate infinite mode of Thought he describes as "the idea of God"; the mediate infinite mode he calls "the infinite idea" or "the idea of all things". The other Attributes (if any) must be conceived in an analogous manner. And the whole Universe or Substance is conceived as one dynamic system of which the various Attributes are the several world-lines along which it expresses itself in all the infinite variety of events.
Given the persistent misinterpretation of Spinozism it is worth emphasizing the dynamic character of reality as Spinoza conceived it. The cosmic system is certainly a logical or rational system, according to Spinoza, for Thought is a constitutive part of it; but it is not merely a logical system — it is dynamic as well as logical. His frequent use of geometrical illustrations affords no evidence at all in support of a purely logico-mathematical interpretation of his philosophy; for Spinoza regarded geometrical figures, not in a Platonic or static manner, but as things traced out by moving particles or lines, etc., that is, dynamically.
