Abstract

The early modern period was the natural historical habitat of the Principle of Sufficient Reason, i.e., the demand that everything must have a cause, or reason. It is in this period that the principle was explicitly articulated and named, and throughout the period we find numerous formulations and variants of the PSR and its closely related ‘ex nihilo nihil fit’ principle, which the early moderns inherited from medieval philosophy. Contemporary discussions of these principles were not restricted to philosophy. “Nothing will come of nothing; speak again” old King Lear tells his daughter Cordelia at the beginning of Shakespeare’s celebrated tragedy, and in early modern science, conservation principles were the order of the day. Within philosophy, Malebranche stipulates that there cannot be an effect without a cause, and Berkeley motivates his idealism by an appeal to ‘ex nihilo nihil fit.’ Were we to try to provide an exhaustive survey the various formulations of the PSR in this period – including the weaker ones – we would be writing an encyclopedia. In fact, one wonders whether any early modern thinker was willing to accept a wholesale rejection of the PSR, i.e., a view which states that no fact requires an explanation. Moreover, the view that many – perhaps most – facts require an explanation seems to be tacitly assumed even by us today, in both our theoretical and colloquial discourse. For these reasons, this chapter will focus on two early modern philosophers who advocated very strong (i.e., virtually exceptionless) versions of the PSR: Benedict de Spinoza and G.W. Leibniz. Following a brief overview of Descartes’s restricted endorsement of the PSR, I will turn to discuss the central features of the PSR in the writings of Spinoza (§2) and those of Leibniz (§3). In the cases of each of these philosophers, we will examine carefully: (i) their main statements of the PSR, (ii) the scope they assign to the principle (i.e., what requires an explanation and what counts as an explanation), (iii) the modal strength they assign to the principle, (iv) the main implications they draw from the principle, (v) exceptions to the principle, and, finally, (vi) the justification of the principle. In §4, we will study a principle, complementing the PSR, namely, the assertion that everything and every fact must have an effect (or as Leibniz would put it: “nothing is sterile”).