Naturalised Realism in the Metaphysics of Science: Hume’s “Mitigated Scepticism” on Causality and Reality

The inception of modern science, in the 17th century, was accompanied by epistemological analyses that see its foundation as laid on observation and experiment — a stance often regarded as excluding (or, at least, devaluating) metaphysics, especially in the English-speaking world. Qualms about metaphysics were already noticeable in Locke’s Essay (1690), and were supposedly deepened by Hume, in the following century. For almost two hundred years, Hume’s philosophy was regarded as radically sceptical concerning metaphysics generally, but particularly about causality and the very existence of an external, objective reality. In this paper, we argue, following a more recent interpretive vein in Hume's scholarship, that Hume’s scepticism about these basic metaphysical issues was effectively “mitigated” (in his own words) by his pioneering adoption of a form of naturalised realism. According to it, belief in both causal relations and in the external world is taken as resulting from the natural operations of the human mind and, in this condition, as being justified, in an epistemologically non-ordinary sense of this notion. As a consequence, epistemology was seen by him as an undertaking akin to the natural sciences, both employing similar empirical methods and metaphysical hypotheses to explore the mind, in the former case, and the physical world, in the latter. Thus, instead of interpreting Hume as one of the forerunners of the anti-metaphysical trend within empiricism, we believe that his wide-ranging project of instituting a “science of man” made some room for metaphysics, as cultivated within the same fallibilistic, naturalistic approach of empirical science itself.