While inquisition manuals may on balance be the best sources for understanding how inquisition worked and changed in the fourteenth century, they must nevertheless be approached with caution. All inquisition records present problems of analysis and interpretation – they were not written to provide the answers to historians' questions – but there are particular traps to avoid with manuals. First, obviously, as with all historical records, one must bear in mind their readership and their historical and social contexts. The inquisition did not exist in a vacuum but, like all historical phenomena, was shaped by its social and political contexts; that is true for both the Practica and the Directorium.

Second, any inquisitor's manual is necessarily normative; it shows how the author believed the inquisitorial process should be carried out, rather than precisely how it operated in practice. This is a bias that can be found in any text-book, and it is found in our two principal manuals. For example, as will be shown in Chapter 4, the manuals see the prime means of detecting heretics as the period of grace, when the heretics can surrender or be denounced, but they do not directly mention the other means, which the evidence shows inquisitors certainly employed. Nor do they discuss explicitly the limitations and realities of inquisitorial power. There was, as it were, an inquisitorial view of reality, a reality constructed by the Church and its inquisitors, which is reflected in many inquisitorial sources. It led those who held it to value highly the authority of the inquisition, and therefore to be reluctant to describe directly the compromises necessary for the inquisition's work. Part 4 of the Practica, which at times eulogises the inquisition, is an example of this high estimation of the inquisition. This view is a filter through which both Eymerich and Gui wrote their manuals, although Gui is more ready to give indirect advice about delicate and difficult issues.

Third, both authors had particular and identifiable aims in writing their manuals, which were wider than the simple transmission of inquisitorial law, procedure and practice. The aim of this chapter is to understand these inherent biases, as well as how the Practica and Directorium were constructed as manuals, so that they can be more effectively used as sources.