Well, it depends, doesn’t it?
Even if you’ve never thought about it before, it’s perhaps not too surprising that the word into is a combination of the words in and to. If you think about any sentence in which you might use the word, it clearly combines the meaning of both:
He walked into the room.
To is there because there’s movement, and to usually comes after verbs of movement. In is there because he ends up in the room. Easy. But, does this mean we can always replace in to with into?
No teacher likes to be observed. I still remember my first teaching practices when I was training to be a teacher. It was terrifying, because I’d never done anything remotely like teaching beforehand, and then suddenly had to stand up in front of a group of strangers and help them understand a list of words. This was made even worse by having an experienced teacher observe me, along with three fellow trainees. Being in that position really makes you doubt yourself. Whenever you see them make a note, you think about what you must have just done wrong, and hesitate about what to do next.
This is the sort of English up with which I will not put.
– Winston Churchill (probably) on an editor mangling a sentence in his memoirs that had ended in a preposition
Can you end a sentence with a preposition? This has long been a subject of debate in grammar cirlces, though currently most people suggest that it’s fine.
Before we look at whether ending a sentence with a preposition is acceptable or not, we should first ask: what is a preposition? They’re tricky little words such as to, at, in, on, under, with, above etc. Basically they’re like connective tissue, or mortar between bricks. Or little tugboats pulling heavy ocean liners around. They don’t seem to do much on their own, but we need them to join the main concepts of sentences together.