1. The Infinitives are indeclinable nouns with non-personal verbal functions, which can be as many as inflection, voice, aspect and even time.
NOTE. Infinitives are, thus, old nouns reinterpreted as verbs.
2. The older Infinitives are the Verbal Nouns, i.e., casual forms inflected as nouns, although sometimes included in the verbal inflection. A Verbal Noun is a declinable substantive, derived from the root of a verb.
NOTE. The difference in the syntax is important; the verbal noun is constructed as a substantive, thus - for example - with the object in the genitive: the killing of a man, as opposed to the accusative with an infinitive, to kill a man.
3. Verbal Nouns are, thus, the normal way to express the idea of a modern Infinitive in Europaio. Infinitives can be nevertheless formed in modern Europaio with the verbal stem (athematic or thematic), being indeclinable; as, deik, to show (showing); es, to be (being); ed, to eat (eating); etc.
NOTE 1. The usual formal condition is that the Infinitive is not already a noun: as in ag, to act, which can only function as infinitive. When the root is already a noun, a thematic stem with -e/o shall form the Infinitive. When this is not possible, then a Verbal Noun has to be used.
NOTE 2. Although each Europaio dialect chose between some limited noun-cases (not presented here) for the Infinitive formation, they were not general in the IE III nor in the Northern Dialects or the languages that followed, and could be easily confused in our system with imperfects, futures and perfects, and with the normal noun inflection.