Such a purpose however would hardly have justified the introduction of the subject here. The motive which dictated its consideration was much more practical. It was hoped that the answer to many species of doubt would be found by referring them to the forms of thought or of philosophy from which they had sprung; that it would be possible to perceive how they might be refuted, by understanding why and how men have come to believe them.(1010) This is a study of mental pathology seldom undertaken. The practical aim of Christian writers has generally suggested to them a readier mode of treating the history of unbelief, by referring its origin to intellectual pride; and, if any margin remained unaccounted for by this explanation, to refer it to an invisible agent, the direct operation of Satan.(1011) Such a method, however true, commits the error, against which Bacon utters a warning, of ascending at once to the most general causes without interpolating the intermediate. It ignores the intellectual class of causes, and omits to trace the subtlety of their mode of manifestation;—a problem equally interesting, whether they be regarded as original causes of doubt, or only as secondary instruments obeying the impulse of the emotional causes. It would have been possible to investigate the subject, by selecting a few leading instances to illustrate the natural history of doubt; but the most likely mode for exhausting the subject, as well as for presenting it in a manner which would fall in with the historic tastes of the age, seemed to be, to treat it by means of a critical history, presenting the antidote by a running criticism; and to ask, frankly and fully, what have been the grounds on which Christianity has been doubted; and what have been those on which the faith of Christians in their hour of peril has reposed; and then finally to gather up the lessons which the history itself teaches. The inquiry has been analogous to the study of the history of a disease; and scientific rigour required that it should be conducted with a similar spirit of fairness towards those that manifest its symptoms. As the physiologist, who wishes to learn the laws of a disease, watches patiently the symptoms in the subject of it, not reproaching the sufferer, even if the malady be self-caused; so in moral diagnosis, the student of mental and religious error must carry out his inquiries in the spirit of cold analysis, if he would arrive at the real character of the intricate facts which he studies. The candour of our examination has not been prompted by any spirit of indifference to truth, nor by sympathy with error; but partly by the demands of historical accuracy, partly by deep pity for those who are the subject of spiritual doubts, even when the doubts are of their own fault.