Picking up a ruler ready to crack some knuckles…
The word ‘to,’ has many meanings. And, depending on the meaning be used, can be different parts of speech.
That’s right, a word can be more than one part of speech, depending on its usage. E.g., ‘snow’ is a noun in “The snow is white,” and a verb in “Will it snow heavily tonight?”
And so, ‘to’ can be a preposition, which is a word that links a noun (or a pronoun or a noun-phrase) to some other word. E.g…
The dog moved closer to the ball. – In this case, ‘to’ is linking ‘door’ to ‘moved’ (How moved? To the ball.) In this case, the preposition is modifying a verb, and thus it is an adverbial preposition.
Mr. Brady may be just another TV dad, but he’s a hero to me. – Link’s ‘me’ to ‘hero,’ and thus, and adjectival preposition.
But ‘to’ can also be part of a verbal phrase, sometimes being called an auxiliary verb. We use it in this way to show the infinitive form of the verb: to run, to snow, to laugh, to cry, to have sex.
And to make things more complicated, ‘to’ can be an adverb as in ‘run to and for,’ or, ‘the unconscious man came to.’
And, ‘to’ has become part of idiomatic phrases which can be parsed word by word, although, the idiom sometimes begs to be taken as an inseperable whole, as in, “Do I have to?” ‘Have to’ is idiomatic since ‘have’ and ‘to’ don’t make any sense by themselves nor would they seem to be able to combine to make the sense of ‘must.’
Peace.
