Substance monism is a very significant part of Spinoza’s philosophy. But after reading the first part of his Ethics, an understanding of his arguments for it eludes me. Specifically, I have trouble wrapping my head around how Spinoza can eliminate the possibility of the following two scenarios:

  1. There exists n>1 substances of the exact same attributes but which have different modes

  2. There exists n>1 substances, all of which have different attributes

Any insight would be appreciated.

1 Answer 1


Option 1 is ruled out by Spinoza's conception of attribute. No two substances can share an attribute, because for Spinoza an attribute both specifies the qualitative 'kind' of an entity, and also its numerical identity. If two or more substances shared an attribute, there would be no reason why one substance is this particular and the other that particular. But that would violate the principle of sufficient reason.

Option 2 is ruled out by Spinoza's conception of God. God is absolute infinite, in the sense of having no outermost boundary or limit. But if there was an attribute God didn't possess, he would have an outermost. Hence if there was greater than 1 substance, it would have to be such that it shares an attribute with God. But that option was already ruled out above.

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