Hume’s philosophy in the Treatise draws a limit to knowledge or understanding. This philosophy will therefore strike some as sceptical. In the final part of Book I, Hume considers how his views are related to the scepticism which has flourished in the history of philosophy. He argues in effect that his views constitute a form of mitigated scepticism and that this should be distinguished from Pyrrhonism or total scepticism.1 He argues, further, that total scepticism arises from an unbridled use of reason. There is in reason a tendency to become autonomous, to work out of relation to our other faculties and therefore to go beyond its natural limits. In this condition, it raises questions it cannot answer, becomes involved in contradictions, and reduces the mind to a universal doubt. Reason, in short, no less than the body, is liable to corruption. The cure is to cast a sceptical eye on reason itself. For this purpose, we need a mitigated scepticism which does not deny the use of reason but which understands its limits. A mitigated scepticism is therefore the cure for a total scepticism. In the course of his discussion, Hume considers our idea of the self and of the independent world. His treatment of these ideas is intended to be parallel to his treatment of causality. He seeks to show, for example, that our idea of an independent world is not produced by reasoning but by the workings of a natural tendency. As we have suggested, however, his treatment is altogether less successful, so that there are passages which run out of control and the author becomes involved in the scepticism from which he seeks to deliver us. It is these passages, as much as any, which support the idea that Hume is himself advancing a total scepticism. We shall return to this point. But first let us consider how Hume opens the final part of Book I.