"To hear" or "to hearing"?

I often see constructions like this one:

I look forward to hearing from you soon.

It seems a little strange to me. In my mind it would look better using the infinitive form "to hear". I don't know if it has something with the verbals... Anyway, what I want to know is which form is correct and why?

Solution 1:

This is not an infinitive. "Hearing from you soon" is a gerund, which functions as a noun.

I look forward to [hearing from you soon].

is the same kind of construction as

I look forward to [my vacation].

Solution 2:

If it were an infinitive, you'd be correct - it would have to be "to hear." But in this sentence, to isn't functioning as part of an infinitive, but simply as a preposition. That has to be followed by a noun or a nominal phrase, and "hearing" is a noun.

Solution 3:

Grammatically speaking, a thing being looked forward to (hearing in this case) should be a noun. Parse it here as the experience of hearing if that makes any more sense to you.

But even though it's a stock phrase in business letters, it is a somewhat odd choice of words for its normal context, where invariably the anticipated event will be reading, rather than hearing.