The lay team of notaries, familiares and others provided the backbone of the inquisition's day-to-day work. The inquisitor was, however, also heavily reliant on his closest clerical assistants, his vicars (deputies), and the more junior friars named as his socii, or companions. The role and powers of these members of the inquisition team have barely been touched on by past scholars, perhaps because they feature so little in inquisition manuals and handbooks. Inquisitors themselves did not spring fully–formed from anonymous mendicant ranks, so aside from the question of how vicars and socii functioned within the overall team, it is necessary to consider whether these posts were in any sense ‘training’ for future inquisitors. This leads on to a discussion of the inquisitor's own cursus honorum.

Despite similarities in both powers and duties, the two posts of vicar and socius were in principle very different. The vicar could – within limits – stand in for the inquisitor himself. By contrast, the socius had a function much more akin to that of a modern-day executive's personal aide. His influence came not from special conferred powers, but from his close personal contact with the inquisitor, and others’ belief that he reflected the inquisitor's own wishes. Given the need for confidence in their performance, the socii of office-holders within the mendicant orders (such as conventual and provincial priors) were elected by ballot of the members of the convent. It seems likely that this applied to the socii of inquisitors too, though they probably had somewhat more freedom to choose who they wanted. The choice of vicar was however subject to advice from the convent hierarchy.

The significance of the clerical support staff has to be considered against the background of the tiny number of full inquisitors responsible for the whole land area of modern Italy. Before 1256, there were only four for the huge Dominican province of Lombardy. Although this number was doubled in March 1256, and increased further by the early fourteenth century, there were in our period at most ten inquisitors in upper Lombardy and three in the new lower Lombard province, created in 1303 by splitting the original Lombard province in two.