Why did the author use "remembering" instead of "remember" in "principles that I think are key to remembering"

Question

I was watching a video about how to learn new vocabulary more easily, but I was stuck at this sentence spoken by the video author:

Now I'm starting with three basic principles that I think are key to remembering English Vocabulary.

I don't understand why the author used remembering instead of remember after to, is it a special grammar rule in this case or what?

Answer 1

to in this case is simply taken as a preposition.

In light of this use, you can replace what is next (together with the gerund) with a noun.

Now I'm starting with three basic principles that I think are key to it.