What are the rules for using “to” with can and want?

Trying to explain to my Spanish-speaking friend the use of can vs. want, I realize I have no idea of rules for the use of "to". Sometimes it's used, sometimes not, I know what sounds right but I don't know why.

I can/will/shall speak. I want to/wish to/hate to speak.

Where can I read up on the use of "to" in these cases?

Solution 1:

We get a lot of questions (particularly on the sister site English Language Learners) about use of prepositions, which are often couched as "which one is right".

What these questions have in common is that they rarely mention the governing word in the title: it's as though the questioners think there is a universal rule, separate from the governing word; so well done for actually telling us the context of your question.

Can is a modal, and like all modals it is followed by a bare verb and never by a "to" infinitive: She can reach it, never *She can to reach it

Want is a full verb, and is followed either by a noun phrase (eg I want a pistachio ice-cream) or by a "to" inifinitive clause (eg I want to eat a pistachio ice-cream). It can never be followed by a bare verb (*I want eat a pistachio ice-cream)

Common Verbs that are frequently followed by a "to" infinitive clause (want, going, trying, got, have) tend to acquire a (non-standard, but widespread) grammaticized contracted form in "-ta/na": (wanna, gonna, tryna, gotta, havta - though it is not customary to write these in this way), and these behave like modals: I wanna eat a pistachio ice-cream.

(One word in that list, have, can also take a past participle, to form perfect tenses; He has seen in. This is different in both syntax and meaning from have taking a "to" infinitive clause).