So recently I've encountered the phrase "seeing it come to life" and while I understand its use and meaning, I do not understand the grammar behind it.
Why is it that the verb "come" is written as "come" rather than "comes"? "Comes" would agree with "it".
You're trying to make the word "it" be a subject. Under a traditional analysis, it simply isn't.
Consider my first sentence. The bare infinitive "be" doesn't agree with any subject, in the same way that the bare infinitive "come" doesn't agree with any subject in your phrase.
The pattern seen here is a direct object with an object complement. An object complement isn't a predicate on its own. Instead, it is another argument of some governing verb. In my example, that verb is "to make". In yours, it's "seeing".
It can be difficult to see when a verb is in its bare infinitive form. For most verbs, that form is the same as the present-tense form which agrees with plural subjects. I used the verb to be in my sentence because its infinitive form doesn't look like any of its finite forms.
You're seeing something come to life, and seeing it be alive. These are infinitives that don't, and can't, agree with any subject.
Because the verb is "come to", not "come" in isolation. "Come to" is a phrasal verb akin to "achieve".
Seeing it "come to" life vs It "comes to" life.
Seeing it "achieve" life vs It "achieves" life.
