The 2nd stage of Old Portuguese, also called Middle Portuguese, is a high period of major changes in the history of the Portuguese language. The changes in deverbal noun formation with the suffixes -mento, -ção and -nça have decisively contributed to the codification of inovative concepts and to the new configuration of the derivational patterns of Modern Portuguese. The motivations of the declin of some suffixes forming deadjectival and deverbal nouns are analised in order to evaluate their conformity with the prototipycal solutions of linguistic change. The solutions adopted by some deverbal nouns sharing the same base but containing different suffixes reveal different pathes, in function of the suffixal resources involved and their ‘internal’ and ‘external’ circumstances.We claim that the unavailability – after the 15th and 16th centuries – of -nça, an archaic and non-learned form, in contrast with the prestigious configuration of the neoclassical -ncia, must be taken as a defining feature of the changes characterizing Middle Portuguese.