Newton’s ‘derangement of the intellect’. New light on an old problem

There is no doubt that in the years 1692 and 1693 Newton underwent a period of severe emotional and mental disturbance, the cause of which has, in our opinion, never been satisfactorily explained. The whole episode has always had something of an air of mystery about it; even the very existence of what Manuel aptly, though rather inaccurately, described as Newton’s ‘Black Year’ was hidden for almost a century after his death and by way of introduction it is relevant to recount here the attitude of some of Newton’s biographers to what, for the sake of convenience and brevity, we will simply call his illness