As an empiricist, Hume believed that all our ideas are originally based on first -hand experience which enables us to grasp the notions of ‘habit, contiguity and association of ideas’. The law of cause and effect is nothing but the psychological interpretation of a sequence of events. For instance, the repeated experience of the conjunction of flames and heat creates an association of ideas, which leads to the idea of ‘heat’: ‘All our ideas are nothing but copies of our impressions, or, in other words, it is impossible for us to think anything, which we have not antecedently felt, either by our external or internal senses.’

Hume applied his observation of human behaviour to his analysis of human knowledge. Hume’s greatest discovery is that belief is not based on deep, undeniable rational sources but, on the contrary, ‘belief consists merely in a certain feeling or sentiment; in something, that depends not on the will, but must arise from certain determinate causes and principles, of which we are not masters.’ This position leads Hume to scepticism as he is forced to admit at the end of his ‘Treatise of Human Nature’ that ‘all our distinct impressions are distinct existences, and the mind never perceives any real connexion among distinct existences.’ Human knowledge is necessarily limited by our imperfect power of reasoning: ‘Reason is the slave of the passions.’ It is, in fact, ‘custom’ or ‘habit’ which is at the origin of our epistemological (related to our knowledge of the physical world), moral and religious beliefs. As far as Nature is concerned, the physical world seems to be subject to chance, due to, firstly, the random character of physical events and secondly, the absence of divine determinism.

Regarding philosophical explanations for the existence of a divinely ordained Creation, Hume attacks the three traditional arguments systematically. Analysing the cosmological argument, he first argues that having no experience whatsoever of a plurality of universes, we cannot speak meaningfully about the creation of the universe we are familiar with. After all, we were not even there when the universe was created. To move from ‘everything that we observe has a cause’ to ‘the universe has a cause’ is, for Hume, too big a logical leap.

His criticism of the ontological argument is very close to Kant’s own reservations about its actual logical validity. For the Scottish thinker, ‘something cannot be defined into existence’ or derive its existence from its assumed perfection. For Hume, and for Kant, existence simply cannot be predicated or presumed without proof. We must go beyond the supposedly attributes or qualities of something and prove its actual ‘naked’ existence, before attaching labels to that presumed existing entity.

Hume develops four critical arguments to the teleological argument in his ‘Dialogues concerning Natural Religion’, published after his death:
The design of the universe cannot be compared to any human design, especially when one considers all the imperfections of the human world. The assumption of an ordered universe is purely gratuitous and not scientifically provable: to speak of ‘design’ in the world implies the existence of a ‘designer’. A great design implies a great designer. There is a ‘great design’ in the world, therefore, there must exist a ‘Great Designer’. However, Hume argues, the world is not ‘great’ in the sense of ‘orderly’ or even ‘perfect’, which leads him to the conclusion that, if a ‘great designer’ actually exists, he must be as imperfect and flawed as his creation. It is, in fact, just as probable that the world was created by design than it was created by pure chance. There is nothing to convince us that there is only ONE creator. What about several creators in charge of different parts of the universe. (possibly a weak argument but several architects sometimes collaborate on the same project). Matter may, after all, be self-ordering and responsible for its own growth and evolution. Despite Hume’s absence of solid scientific proof to support his argument, he is putting forward a kind of pre-Darwinian argument in supposing the self-regulating character of the natural world. Instead of comparing the world to a sophisticated machine, like Paley’s watch, Hume suggests comparing it to a carrot, as an example of Nature’s growth and generation.