Why are some verbs, such as “immineo, -, -, ere” listed in the Latin dictionary with only two principle parts?
There are certain verbs in Latin (and Ancient Greek, for that matter) which are known as defective, meaning that they lack certain principle parts. In most instances, it is simply that we don’t have an attested use of a particular tense – immineo is never found in the perfect, for example. This does not necessarily mean that they did not exist in the original Latin, but instead that they are not included in the texts we have available. Given the already formal and constructed nature of Latin (Classical Latin was restricted to formal occasions – at other times, Vulgar Latin, a much simpler form used by commoners, or Ancient Greek, among the wealthier classes, was used) it is difficult to say whether non-extant forms could potentially exist, or if there was a set limit of what forms were allowed to be used. In short, it may be that we just don’t have examples of a tense, or that Classical Latin didn’t allow for their use. There are also some rare verbs, such as memini and coepi, which do
