Spinoza's Ethics, Bk. I

Substance and Attributes

Before Spinoza proceeds to prove that God is the only substance (Bk. I, Proposition 14), he provides definitions of substance, attribute and mode that require some interpretation.

SOME DEFINITIONS EXPLAINED

(I) Substance: "that which is in itself and is conceived through itself" (p. 158)

To say that a substance is "in itself" is to say that it exists all by itself. That is, it exists independently of anything else whatsoever. It is completely self-sufficient. This means that it does not need anything else to bring it into existence or to sustain it in its existence. It is not dependent on any external cause. It also means that it does not cause any other substance to exist or to continue to exist, either. A substance does not enter into any causal relations with any other substance in any form whatsoever. It is completely causally 'isolated', as it were.

(Thus, if it were possible for there to be two substances, then these two substances would not be causally related to each other at all -- they would exist in perfect isolation from each other.)

To say that a substance is "conceived through itself" is to say that the concept of it does not require the concept of anything else whatsoever. The concept of a substance, like the substance itself, is also self-sufficient, or 'isolated', in terms of being intelligible all by itself.

(Thus, if it were possible for there to be two substances, then the concepts of these two substances would be completely unrelated to each other -- each would be fully intelligible all by itself.)

(II) Self-caused: "that whose essence involves existence... that whose nature can be conceived only as existing" (p. 158)

Although this is merely a definition of self-caused, Spinoza will later demonstrate that substance is self-caused (causa sui), i.e. that the nature or essence of substance is, or involves, existence. The point is that a substance is not a substance unless it exists.

"Non-existing substance" is a contradiction in terms, like "square circle". "Existing substance" is a tautology, like "tall skyscraper" or "creamy cream".

X is a substance ––> X exists.

This may be called the Ontological Argument for the Existence of Substance.

We can now conclude that there are three conditions for something's being a substance:

(i) It must exist in itself.

(Another way of putting this is that it must always be a subject and never be a predicate. It is always the subject of predication, and never predicated of something; it remains the same through changes in predication.)

(ii) It must be conceived through itself.

(Another way of putting this is that it must be understood or explained through itself alone, without involving any conception of another thing.)

(iii) Its nature must be conceived as existing.

(It must be self-subsistent or self-caused (causa sui).

(III) Attribute: "that which the intellect perceives of substance as constituting its essence"

Every substance must have an essence or nature. There cannot be an essence-less, or nature-less, substance. However, in order to characterize the essence of a substance, it needs to be conceived in a certain way. This certain way to conceive the essence of a substance is an attribute.

The two attributes of substance that we know are (a) thinking, and (b) extension. Spinoza implies that there are an infinity of attributes, but that we only know these two attributes.