How would you say He started to speak?
Would that be Li komencis paroli?
In other languagues there is normally a particle next to the infinitive form: he started to speak (English); comenzó a hablar (Spanish); er fing an, zu sprechen (German).
How would it be with the verb fini?
Yes, you just say komencis paroli with no extra particle. If you search for this in the Tekstaro there are many examples, such as this one from Zamenhof’s translation of Andersen’s fables:
Nun unu el la burĝoj komencis paroli pri la terura pesto, kiu furiozis antaŭ kelke da jaroj
It’s the same for fini. Here is an example from Gerda Malaperis.
Gerda sentas sin pli bone. Ŝi ĵus finis manĝi.
I think the only time where you would translate the to before an infinitive in English is when it could be replaced with “in order to”. In that case you can add por before the infinitive. For example “I jumped to avoid the car” could become:
Mi saltis por eviti la aŭton.
Of course ekparoli is far better, but an infinitive is fine too.
ek stresses a point in time, whereas komencis could be a duration. "far better" is not really what I meant; ekparoli is more better display of language power, using Esperanto to its fullest. Possible for "start to read" = eklegi, "start to write" = ekskribi. Definite for "stand up" = ekstari, "sit down" = eksidi, "fall asleep" = ekdormi.
If the purpose of the question is to find a parallel in a national language, consider that the infinitive in Esperanto often corresponds to the -ing form in English: he started speaking.
This rule of thumb often works with other verbs.
The tricky part is to know when you do need a little word (like por) - but that's answered here:
