I've been studying Esperanto for awhile, but I'm still far more fluent in Spanish than I am in Esperanto, and English is my native language. I sometimes find myself trying to avoid interference with both English and Spanish, but I can usually clear up my questions fairly quickly. I'm having a harder time with this one.

I'm trying to decide whether to use an infinitive (-i) phrase or an imperative (-u) phrase when using expressions about wanting (or not wanting) someone to do something. English uses infinitives, Spanish uses the subjunctive (which forms an imperative), and I'm finding BOTH forms in various people's Esperanto---is one correct and the other not? Or is one more customary or stylistically preferred than the other? Here are some examples:

"I want him to come now." Should this be "Mi volas, ke li venu nun" (seems natural)? Or could it be "Mi volas lin veni nun" (or even "Mi volas al li veni nun")?

How about this one: "I asked you to do that." Should this be "Mi petis, ke vi faru tion" or is it correct to say "Mi petis vin fari tion" or even "Mi petis al vi fari tion"?

Or what about "He told you to leave"? Should that be "Li diris, ke vi foriru", "Li diris vin foriri", or "Li diris al vi foriri"? Is there more than one correct way? What about customary style?

AND FINALLY, what about the NEGATIVE of these examples--if you DON'T want someone to do something? Do the rules change?

"I don't want him to come now"--Should it be "Mi ne volas, ke li venu nun" (seems a little odd, since -u usually expresses what you DO want), "Mi ne volas lin veni nun", or "Mi ne volas al li veni nun"? Or do I have to make it "Mi volas, ke li ne venu nun" in order to make it sound right?

"I didn't ask you to do that"---(A)"Mi ne petis, ke vi faru tion"? (B)"Mi ne petis vin fari tion", (C)"Mi ne petis al vi fari tion"? What is your verdict, Experanto experts? Only A is correct? All of the above? Both A and C are correct? ????

Jumping to the last one...what would "he told you NOT to leave" be? "Li diris, ke vi ne foriru", "Li diris al vi ne foriri" or "Li diris vin ne foriri"?

Sorry for the long-winded question, but I'd really like to get this question answered and laid to rest once and for all. Thanks!

Polaris:

"I want him to come now." Should this be "Mi volas, ke li venu nun" (seems natural)? Or could it be "Mi volas lin veni nun" (or even "Mi volas al li veni nun")?

How about this one: "I asked you to do that." Should this be "Mi petis, ke vi faru tion" or is it correct to say "Mi petis vin fari tion" or even "Mi petis al vi fari tion"?

Or what about "He told you to leave"? Should that be "Li diris, ke vi foriru", "Li diris vin foriri", or "Li diris al vi foriri"? Is there more than one correct way? What about customary style?

AND FINALLY, what about the NEGATIVE of these examples--if you DON'T want someone to do something? Do the rules change?

"I don't want him to come now"--Should it be "Mi ne volas, ke li venu nun" (seems a little odd, since -u usually expresses what you DO want), "Mi ne volas lin veni nun", or "Mi ne volas al li veni nun"? Or do I have to make it "Mi volas, ke li ne venu nun" in order to make it sound right?

"I didn't ask you to do that"---(A)"Mi ne petis, ke vi faru tion"? (B)"Mi ne petis vin fari tion", (C)"Mi ne petis al vi fari tion"? What is your verdict, Experanto experts? Only A is correct? All of the above? Both A and C are correct? ????

Jumping to the last one...what would "he told you NOT to leave" be? "Li diris, ke vi ne foriru", "Li diris al vi ne foriri" or "Li diris vin ne foriri"?

Sorry for the long-winded question, but I'd really like to get this question answered and laid to rest once and for all. Thanks!

Any time someone wants someone ELSE to do something, use the -u form. Just as in Spanish you'd use the subjunctive. "I want to go" there are two actions; 'want' and 'go.' and the person (going to be) doing both is the same. Similarly, "He wants to go." So in Esperanto and Spanish, the infinitive is used. (FYI, in Greek and Romanian et al., you'd use the subjunctive or equivalent for both verbs).
In "I want you to go" you use the -u form (or the subj in Spanish).
As to the negative, which ever action is negative, put "ne" in front of that verb, whatever form it takes. In your mtp choice, A is correct, and the answer to your ? is "A"...the answer in the penult paragraph is #1

I've never seen "mi volas lin veni" but some other verbs like peti and ordoni can be fine with the infinitive and appear quite frequently. If you search Tekstaro with the following string you'll see many examples:

\\b(pet|ordon)[iaou]s? [mnvlŝi]l?in \\w+i\\b

Polaris:I'm trying to decide whether to use an infinitive (-i) phrase or an imperative (-u) phrase when using expressions about wanting (or not wanting) someone to do something.

If we use a complete clause to express a wish, we use the imperative with a comma and ke before the clause. However, if a complete clause is not used then an infinitive can be used. That is the case in your examples. So I could translate them

Polaris:"I want him to come now."

Mi volas lin veni nun.

Polaris:"I asked you to do that."

Mi petis vin fari tion.

Polaris:"He told you to leave"?

Li ordonis vin foriri.

Polaris:what about the NEGATIVE of these examples?

Use ne before the verb.

However I could also translate them using complete clauses e.g. Mi volas, ke li venu nun.

You may find it helpful to consult sections 477, 846(a), and 944-945 of Butler's Step by step.

You can feel free to use the -u form or the -i form.

I mainly use the -u form. You will find many cases of the use of both in Esperanto literature. It's true that with ordoni and peti in particular, the -i form is clearly more popular in the Tekstaro. But if you expand the search to all verbs, you find many, many uses of the -u form. Use the form that feels comfortable to you.

erinja:It's true that with ordoni and peti in particular, the -i form is clearly more popular in the Tekstaro. But if you expand the search to all verbs, you find many, many uses of the -u form.

This could be something to do with this:
I-verbs with a different subject - Note, that this kind of thing is only possible after certain types of verbs, such as 'peti', 'doni', 'ordoni' etc...

I don't think it's possible to say "Mi volas lin veni nun" - this sounds a bit weird to me. I would always say: Mi volas, ke li nun venu.

I haven't found the exact page in PMEG to confirm this yet, but that's my impression at the moment.

I still haven't found the exact PMEG page to describe why 'Mi volas lin veni' is not possible, but how about this for an example:

I want him to understand = Mi volas, ke li komprenu.

Now, there's no way we could write that as 'Mi volas lin kompreni', as that would mean 'I want to understand him' (and there's no other way of understanding this sentence!)

Chainy:"Mi volas lin veni nun" - this sounds a bit weird to me.

Same here. But for me the best reason to avoid this type of usage, apart from the fact nobody really speaks that way, is that it's potentially confusable; if the infinitive were a transitive verb the meaning would be something completely different. For example "mi volas vin manĝi" would not mean "I want you to eat" but "I want to eat you". I believe this may go some way to explaining why voli always gets the u-mode treatment, unlike the ones on that PMEG page you cite.

Polaris:How about this one: "I asked you to do that." Should this be "Mi petis, ke vi faru tion" or is it correct to say "Mi petis vin fari tion" or even "Mi petis al vi fari tion"?

All of those versions are fine. I suppose it's a case of whether the sentence could possibly be understood in the wrong way or not! In all the examples you give here it is clear that the verb 'fari' relates to 'vi'.

Ok, so you could say the same about 'Mi volas vin veni', but that's only in this particular case (if you replace 'veni' with 'kompreni', then this changes things, as I mentioned earlier) I think verbs like 'inviti' and 'ordoni' can be used in this way (eg. Mi invitis lin veni) simply because it doesn't matter what verb you replace 'veni' with in that sentence and it will always clearly relate to 'lin'...

tommjames:

Chainy:"Mi volas lin veni nun" - this sounds a bit weird to me.

Same here. But for me the best reason to avoid this type of usage, apart from the fact nobody really speaks that way, is that it's potentially confusable; if the infinitive were a transitive verb the meaning would be something completely different. For example "mi volas vin manĝi" would not mean "I want you to eat" but "I want to eat you". I beleive this may go some way to explaining why voli always gets the u-mode treatment, unlike the ones on that PMEG page you cite.

You beat me to it! I posted just seconds after you. I like your explanation, the fact that the use of transitive verb changes the meaning. That's pretty much what I was getting at, too!