The comprehensive statement for the above is, that there is only one infinite substance that excludes from itself all determination and negation, and is named God, or nature.
2. Besides the infinite substance or God, Descartes had assumed two other substances created by God, viz., mind (thought), and matter (extension). These two Spinoza considers in the light of attributes, though, like Descartes, he receives them empirically. What, now, is the relation of these attributes to the infinite substance? This is the severe question, the tendon-Achilles of Spinoza’s system. They cannot be essential forms in which the substance may manifest itself or appear, for this would make them determine the essence of the substance, which would contradict its conception as already given. Substance, as such, is neither understanding nor extension. If, then, the two attributes do not flow out of the essence of the substance, and do not constitute the substance, there remains only one other supposition, viz., that they are externally attached to the substance; and this is, in fact, Spinoza’s view. Attribute, according to him, is that which the understanding perceives in the substance as constituting its essence. But understanding, as Spinoza expressly says, does not belong to substance as such. Attributes, therefore, are those determinations which express the essence of the substance only for the perceiving understanding; since they express the essence of the substance in a determinate way, while substance itself has no determinate way of being, they can only fall outside the substance, viz., in the reflective understanding. To the substance itself it is indifferent whether the understanding contemplate it under these two attributes or not; the substance in itself has an infinity of attributes, _i. e._ every possible attribute which is not a limitation, may be predicated of it; it is only the human understanding which attaches these two attributes to the substance, and it affixes no more than these, because, among all the conceptions it can form, these alone are actually positive, or express a reality. God, or the substance, is therefore thinking, in so far as the understanding contemplates him under the attribute of thought, and is extended in so far as the understanding contemplates him under the attribute of extension. It is, says Spinoza—using a figure to express this relation of substance to attribute—it is, like a surface reflecting the light, which (objectively taken) may be hot, though, in reference to the man looking upon it, it is white. More accurately substance is a surface, standing opposite to a beholder who can see only through yellow and blue glasses; to whom, therefore, the surface must appear either yellow or blue, though it is neither the one nor the other.