I examine verbal prefixation analyzing the functional changes of the Latin ad- prefix from Classical Latin to Italian. In order to conduct the research properly I needed to separate the verbs in ety- mological groups directly derived from Latin (Classical, Vulgar or Late Latin) from the verbs created in the Romance period and the Latin loan verbs. The different origin of the verbs influences our expectation regarding the analyzability of a given verb (the recognisability of the prefix as an independent element and its semantic value - which can be different from that of its Latin origin). This division is not as clear cut as it seems to be, because, in the case of the Italian, phonetic evidence in favour of one group or another is often missing. I present the possible solutions I found for the grouping problems using semantic evidence, comparison with the other Romance languages, dating of the given verb, etc. Furthermore, I highlight the general and specific factors which determine the assignment of a certain verb to a certain group in order to obtain a precise but still flexible set of verbal categories.