I was looking the pages of the prepositions in the PIV, like el, tra or kun, and a question came to my mind. How the difference is made between morphemes and prefixes? My hypothesis is that if there is no other morpheme (so only affixes and finales), the preposition plays this role. But whenever there is another morpheme, it is considered a prefix. Is this correct?
Edit: As my first message is not very clear, let’s see an example. On the page el of the PIV, there are three big sections: (I) Prepozicio, (II) Memstara morfemo, (III) Prefikso. In section I, there are some definitions of the preposition. In section II, some examples were the morpheme is used only with suffixes (-ig-, -il-) or finales (-e, -i, -o). Finally, in section III, el- is used as suffix, and not a morpheme anymore (elveturi, elpreni, elfini). My question is: is el- considered as a morpheme unless there is root?