My current doctoral research is about the mining societies in Northern and Central New Spain during the 18th century, and especially the region of Zacatecas, Fresnillo and Sombrerete. Within this particular context, I centred my study on the lower classes, a rather heterogeneous social group composed of castas, ladinos and poor Spaniards. This definition leads the reflection towards the analysis of the social stratification from of a socio-economical perspective. However, the case of the poor Spaniards, their behaviour and the way they tend to reject the mestizos and other castas (as potential spouses for instance), stressing on their ties to the more powerful group of the Creoles in the process, indicates that the socio-racial component of the social stratification should not be ignored, at least as far as individual and collective mentalities are concerned. This point of view orientates a questioning about the formation of the colonial society and introduces the notion of the perception of one another as well. The confrontation between the colonial reality and the lower classes' perception can be a way of answering this interrogation. The result of this work is the depiction of an extremely complex and fluid society in which several levels of stratification (real / perceived) add up to produce a social mosaic.