In A Study of Spinoza\u27s Ethics, Bennett provides an analysis of what he calls Spinoza\u27s \u27offical argument\u27 of substance monism. The official argument is Bennett\u27s interpretation of the demonstration of 1P14, and his criticisms of it are powerful ones. This paper addresses one aspect of Bennet\u27s criticisms. A premise of the official argument is the conclusion of 1P5, that there cannot be two substances with an attribute in common. Bennett argues that 1P5 is insufficient to support 1P14. This paper argues that a correct understanding of Spinoza\u27s version of the identity of indiscernibles reveals that 1P5 is sufficient to support 1P14 and Spinoza\u27s argument for substance monism
