This study has two aims. The first is to offer an account of the minimal presuppositions of historical knowledge from the point of view of a particular possibility. There are many accounts of the conditions of historical knowledge available. Most of them accept, either explicitly or implicitly, that these conditions must include some general assumptions about human nature, which serve to provide historical knowledge both with a certain kind of intelligibility and with a general support for the kinds of reasoning upon which it is normally thought to depend. They thus support but, at the same time, constrain the kind of knowledge which historians can provide. It must be at least a conceptual possibility, however, that human nature itself may have changed, to a greater or lesser extent, over time. It would seem unreasonable, therefore, to pre-empt the decision whether this possibility has or has not actually occurred, simply through adopting certain limiting assumptions about human nature as a condition of historical knowledge. Whether or not, or to what degree, such changes have actually occurred ought to be a factual matter rather than one the answer to which follows from methodological considerations alone. One aim of this study, therefore, is to investigate the problem whether an account of the presuppositions of historical knowledge can be reached which will allow it to be a factual matter whether, and to what degree, human nature may have changed in the course of its history.