Spinoza , the No Shared Attribute thesis , and the Principle of Sufficient Reason

1 Introduction According to Spinoza, 'In Nature there cannot be two or more substances of the same nature or attribute' (IP5). 1 Call this the 'No Shared Attribute' thesis, 2 hereafter NSA. It is widely recognised (indeed, virtually undeniable) that NSA plays a crucial role in Spinoza's argument in The Ethics for his version of substance monism—for the view that there exists only one substance, God or Nature—although there is some dispute concerning just what role that thesis plays and just how the relevant argument should be understood. Unfortunately, however, the case that Spinoza offers in support of NSA faces a notorious objection, dating back at least to Leibniz. 3 The Leibnizian objection, which I shall explain shortly, is often presented as decisive. Faced with it, Steven Nadler, for example, concludes unequivocally, 'Leibniz is right'. 4 In this short paper, having offered a brief reconstruction of Spinoza's argument for substance monism emphasising the important part that NSA plays in it, I shall suggest what I think is a novel response to that objection, one that is faithful both to the spirit of Spinoza's work and to the letter.