Selection from – Part II. On the Nature and Origin of the Mind (Page 4)
Spinoza's Words: (as (Deus sive Natura) contains all, it also contains thought)
Proposition I. Thought is an attribute of (Deus sive Natura), or (Deus sive Natura) is a thinking thing.
Proof.—Particular thoughts, or this and that thought, are modes which, in a certain conditioned manner, express the nature of (Deus sive Natura). (Deus sive Natura) therefore possesses the attribute of which the concept is involved in all particular thoughts, which latter are conceived thereby. Thought, therefore, is one of the infinite attributes of (Deus sive Natura), which express (Deus sive Natura)'s eternal and infinite essence . In other words, (Deus sive Natura) is a thinking thing. Q.E.D.
Proposition. II. Extension is an attribute of (Deus sive Natura), or (Deus sive Natura) is an extended thing.
Proof.—The proof of this proposition is similar to that of the last.
Comment:
It is hard not to part from Spinoza here, at one of his important propositions. But the words (Deus sive Natura) is a thinking thing simply evokes some conceptual resistance. It is not difficult to agree with Proposition II and think of (Deus sive Natura) as having a physical existence. After all we are part of it and it is all around us all the time. But to conceive of Nature itself as a "thinking thing" seems a stretch.
Yet if we consider that thinking things are a part of Nature perhaps then we can give Spinoza some slack and agree, albeit with a nagging reservation, that (Deus sive Natura) has a thinking component (us) and by extension is a thinking thing, or that thought is one of its infinite attributes.