Proposition 7 of Spinoza's Ethics book 1 says that 'it pertains to the nature of substance to exist'. This is proven by using (the corollary to) Proposition 6 to say that nothing can produce substance. From which one then concludes that substance much cause itself, end hence existence is part of its essence.

My issue is that i don't we see why it follows that a substance much cause itself, simply because it cannot be produced. Assuming the principle of sufficient reason (which i guess Spinoza does) I can see that this holds if we assume additionally that the substance under consideration exists, because then the substance must have a cause. So perhaps Proposition 7 should read 'If a substance exists, then it pertains to the nature of that substance that it exists'. But if one adds this extra assumption of existence then one can no longer use Proposition 7 to prove the existence of 'god' in Proposition 11.

Any insights on where i am going wrong are very welcome.

  • 1
    Does this answer your question? How does Spinoza deduce substance must cause itself? Commented Sep 1, 2023 at 7:20
  • I agree that this is more or less the same question, but the answer is not complete in my opinion. When we arrive at Proposition 7 we have not yet proved that there is only one substance. So even if Spinoza assumes (using Descartes) that some substance exists, it doesn't mean that all substance exists.
    – Morten
    Commented Sep 1, 2023 at 16:57
  • By definition 3 of substance extended from Aristotle's hylomorphic usage of substantial form, is certainly substantial thus not nonexistent (empty) colloquially, and apparently substances act as ontological commitment here thus by default they have existential import (to be is to be a value of a bounded variable), wherefore your added if clause is not needed. Of course if you're a skeptic denying such ontological commitment, even Spinoza couldn't spin enough to convert you since you’re not in materially adequate harmony with his axioms and definitions, yet... Commented Sep 2, 2023 at 0:50
  • I am trying to deduce Spinoza's Propositions in a purely logical way, using only the Axioms and Definitions, without assuming anything else. It seems like this is not possible. The accepted answer to Spinoza's proof of God basically makes the same point as I am.
    – Morten
    Commented Sep 2, 2023 at 7:58
  • 1
    If you know the conventional FOL with nonempty domain then think in minute details do you ever need to add an additional 'if exists' clause to any member of the said domain? Yet nothing can prevent one from keeping skeptical about the implicitly assumed existence in the first place. Remember nothing in the sky is printing explicitly what's the right answer should be, as all ancient wisdoms recommend know thyself, only you epistemically claim truth ultimately... Commented Sep 2, 2023 at 18:03


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