Augustine propounds a subjective definition of a miracle: it is ‘whatever is hard or appears unusual beyond the expectation or comprehension of the observer’. It is only our habits of mind, therefore, that prevent us from seeing the entire cosmos as the miracle that it is, and that it would appear to be to someone who could see for the first time. In the medieval period the idea arises that a miracle is something special, ‘contra consuetum cursum naturae’ (contrary to the usual course of nature). The rise of the concept of hard, mechanical laws of nature in the 17th century set the stage for the definitive account of Hume in his famous essay ‘On Miracles’ (1750): ‘A miracle may be accurately defined, a transgression of a law of nature by a particular volition of the Deity, or by the interposition of some invisible agent.’ Hume argues that it can never be reasonable to believe in such an event on the evidence of human testimony, at least when that testimony is being used in support of a system of religion. For a miracle needs to be quite outside the normal run of things, whereas human ‘knavery and folly’, the kind of thing that leads to false or misunderstood reportage, is a recognized and regular natural occurrence. So the chance of any report being due to knavery or folly is always greater than the chance of it being due to an event that is quite outside the normal run of things. Hence, they provide the better explanation of the testimony. Hume was aware that a consilience of independent and otherwise creditable testimonies might reasonably lead to people supposing that something they would have regarded as miraculous has actually happened, but he thought the condition was never met in religious contexts, where enthusiasm, piety, and other emotions clouded judgement.