What does Spinoza mean in propositions 11,12 and 13 in part 2 of the ethics?

Question

In the propositions prior to these Spinoza was discussing the way the human soul was 'constituted' by another finite idea of an existing thing, and also about how the human soul was again 'constituted' by the mode of though and by god. Hence it seems that constitutes refers to the same relation of dependence that Spinoza talks about in the first part, of the substance god being cause of the existence of every thought, and thoughts themselves (including human soul), having casual relationships ultimately dependent on god. however in 11-13 he turns to discuss the 'first' thing that constitutes the idea of the human soul, which he takes to be the idea of the body, and claims that all the affects of the idea of the body must exist in the thing that depends on it, the human soul.

that's what I seem to understand from the text, however I'm not sure about it and the argumentation is completely undecipherable for me. Thanks for your help.

Answer 1

See Michael Della Rocca (editor), The Oxford Handbook Of Spinoza (Oxford University Press, 2018), Chapter 5 The Building Blocks of Spinoza’s Metaphysics: Substance, Attributes, and Modes by Yitzhak Y. Melamed.

One of the major questions of metaphysics throughout its history has been: What is? Spinoza has an astonishingly brief answer to this question: God. All that is, is just God (and his qualities).

Spinoza’s God has infinitely many qualities that constitute, or are conceived as constituting, his essence, while the other qualities of Spinoza’s God, though not constituting God’s essence, follow necessarily from God’s essence. Spinoza calls the former “Attributes [attributa]” and the latter “Modes [modi].”

Thus, there is substance: God, with qualities constituting his essence (attributes).

Def.1.IV. By attribute, I mean that which the intellect perceives as constituting the essence of substance.

Def.1.V. By mode, I mean the modifications of substance, or that which exists in, and is conceived through, something other than itself.

Thinking and extension are attributes of God [Prop.2.I and 2.II].

Prop. 2.VI. The modes of any given attribute are caused by God, in so far as he is considered through the attribute of which they are modes, and not in so far as he is considered through any other attribute.

Bodies are modes of extension [Def.1.I] and ideas are modes of thinking [Ax.2.III].

In conclusion, ideas are modes of thinking that in turn is an attribute of substance [God]: we can say that ideas are waves on the "surface" of thinking, in the same way as bodies are waves on the "surface" of extension and both, thinking and extension, are the dual aspects of unique substance.

Thus, from:

Prop. 2.XI. The first element, which constitutes the actual being of the human mind, is the idea of some particular thing actually existing.

we have that ideas [Def.2.III "the mental conception which is formed by the mind"] of existing things ["particular thing actually existing"] are modes of [constitute] the mind of an existing human.