Came across an interesting little paragraph in the PMEG! Scroll down to the paragraph that starts:
“Ĉefverbecaj I-verboj aperas ankaŭ en iaj mallongigitaj esprimoj de dubo aŭ hezito. “
Which means: mainverb-like I-verbs also appear in some shortened expressions of doubt or hesitation.
So normally the “i” form of a verb isn’t used as the main verb in a sentence; it doesn’t have any mood or tense of its own! The “i” form, is the infinitive, the base form:
- ami = to love
- kuri = to run
- fajfi = to whistle
And when you want to use them in an appropriate tense/mood, you alter them:
- Mi amas Esperanton = I love Esperanto
- Kuru! = Run!
- Li fajfis la tutan tagon = He whistled the entire day
But one of the ways in which I-verbs do occur as the main verb is in these expressions of doubt or hesitation. And they’re normally shortened versions of what you could express, say with a “u-verb” (see previous post). Example from that PMEG page:
- Kion fari? = What to do?
- Kion mi faru? = What should I do?
See how we kinda do it in English too in the translations? It seems like the usage is often conversational shortening. So maybe:
- “Savu nin!”, ”Sed la meloj estas nevenkeblaj! Kiel mi povas savi vin? Peti ilin ĝentile?” = “Save us!”, “But the badgers are invincible! How can I save you? Ask them nicely?”
So the “peti” would be a main verb there, all by itself.
Rather than “ĉu mi petu ilin ĝentile?” = “Should I ask them nicely?”, the full version.
And that’s how I understand the usage… You can see how it changes in English too!