David Hume is known for being a sceptical philosopher, but his remarks about the different forms of scepticism and the basis of his own philosophical system are not oftenly studied together. The "careless manner" in which Hume wrote most of his works seem to be contagious among his interpreters, who associate cursorily his claims on scepticism with his common sense philosophy. I explain how Hume's ideal of a scientific philosophy lays in a secondary level because of the sceptical basis of his whole system, especially fictionalism and atomism regarding mental contents. It is only the inexplicable nature of our mind that completes through imagination the insufficiency of the experience data. His elucidations on scepticism fitt better with his common sense mentality, where Nature again has a decisive role, than with the deep problems of the relation between mind and external objects.