This article seeks to analyse the relations established between slaves and freed slaves and written knowledge, based on the period between 1731 and 1750 and on a quantitative survey of documents produced by the County of Rio das Mortes, Minas Gerais. The signatures on these documents were considered as valid data for evaluating the degree of literacy of those capable of signing their names. The autographic data were collected from criminal proceedings and wills, after the original signatures had been qualified with the help of a set of signatures. Other sources were the publishing, in an eighteenth century periodical, of information on the sale or escape of slaves given that some of the news items informed whether or not the slaves were literate. Throughout the period analysed, it became apparent that those who had specialized jobs, like tailors, masons and carpenters, were the ones who dominated the techniques of reading and writing.