 The relative merits of the senses, reason and faith for attaining truth and the guidance of life were a significant issue during this period. As noted above James Tyrrell recalled that the original impetus for the writing of An Essay Concerning Human Understanding was a discussion about the principles of morality and revealed religion. In Book IV Chapters 17, 18, and 19 Locke deals with the nature of reason, the relation of reason to faith and the nature of enthusiasm. Locke remarks that all sects make use of reason as far as they can. It is only when this fails them that they have recourse to faith and claim that what is revealed is above reason. But he adds: