This may be important for example for the affix -iĝ-, which has two somewhat different main uses depending on whether it's derived from a verbal or nonverbal root (further dividing between adjectives, adverbs etc.) But how do I tell whether something was, for example, an adjective or a verb, when removing that I'm left with the root only?
There are many roots which can easily form an adjective or a verb. Usually the two definitions lead to mutually compatible understandings:
la fenestro fermiĝis = "la fenestro fermis sin" aŭ "la fenestro iĝis ferma"
but I think there are examples (here's one slightly constructed) in which they would mean something different:
la fadeno ĵus finiĝis →
la fadeno finis sin (the thread finished)
The thread (in computer terminology) might have finished all its tasks and exited, yielding the control back to the computer, thus "ending itself".
la fadeno iĝis fina (the thread became "final", or would that be "la fina"?)
Here I'm using the meaning of fina as in fina venko: the thread is still running, but is the final one, when it finishes, the whole program will be done.
The difference is clear, in 1. my thread has terminated while in 2. it is still running. Of course there are better expressions for each, but that hinders the question. How do I tell, decomposing a word like finiĝis to fin-iĝ-is, whether the fin is a "verbal root" or a "nonverbal root", to apply the definition from the ReVo?
I'm not meaning to ask about this particular one, but generally: when the same Esperanto root can be used to form various parts of speech, is one of them always considered primary and the others derived from it? How do I find which is which?