Dinh-Vinh Colomban

In his early manuscripts of Elementa juris naturalis (1669-1671), Leibniz looks for normative definitions of legal and moral categories. In this context, he is postulating a “presumption of justice”. To ground this presumption, Leibniz devises several conceptions of probability which lead to epistemological and metaphysical issues. Leibniz then needs to hold together two conceptions of probability with different objects and epistemic values. On the one hand, probability is grounded on an a priori analysis of logical and abstract possibilities, but on the other hand, it is grounded on the a posteriori inference from an examination of the actual empirical world. This duality means that “probability” for Leibniz therefore resists any characterization under a single epistemological conception.

At the end of 17th century, probability calculus paved the way for the mathematization of moral certainty which led to a rethinking of the classical categories of certainty. Jacob Bernoulli’s Ars Conjectandi (1713) outlined a new epistemological model based on the mathematical measurement of probability and a new way of approaching the problem of uncertainty of knowledge. Bernoulli’s “art of conjecturing” posits probability as an irreducible property of certain fields and modalities of knowledge, but one that can be objectified through mathematical measurement and thus positively integrated into knowledge as an objective property. Between the practical field of decision-making for action and the theoretical field of natural philosophy, Bernoulli’s art of conjecturing seeks to develop a new epistemological space that challenges these traditional disciplinary boundaries.

For Margaret Cavendish, knowledge can only amount to probability and never to certainty. Cavendish’s probabilism might seem to echo some of the stances of the Royal Society about the uncertainty of knowledge in natural philosophy. However, Cavendish’s probabilism is grounded in her metaphysical conception of nature and in the ontological properties she attributes to matter, which are in stark contrast with the empirical and experimental method of the Royal Society. Cavendish’s probabilism is metaphysically grounded insofar as she claims that the probabilistic nature of any discourses in natural philosophy can be explained by and integrated into her metaphysical conception of nature. Therefore, we should be careful when using Richard Popkin’s category of “constructive or mitigated scepticism” from his History of Scepticism to label Cavendish epistemology, as it has been the case sometimes in the literature on Cavendish.