Into or in to? It’s a common question, but luckily this is one grammar issue that’s easily clarified.
Into is a preposition which typically specifies some sort of motion, movement, or direction.
I placed my books into my bag.
A writer, an editor, and an agent walked into a bar.
Dip your pen into the bottle of ink.
In each of those examples, into was used to show movement or direction. A sentence that’s correctly using the word into likely answers a question of where.
Into where did I place my books?
Into where did they walk?
Into where should you dip your pen?
When you see the words in and to next to each other, that’s just a coincidence. In would often be part of a phrasal verb and to would be part of an infinitive or used as a preposition.
We checked in to the hotel. In this example, in is actually part of the phrasal verb checked in and to is a preposition telling us where the verb’s action took place.
I went in to escape the cold. In this case, despite in not being part of a phrasal verb, we keep in and to separate because to is part of the infinitive to escape. You’re not answering a question of where; you’re answering a question of why.
If you said, “I went into the house,” into is one word because it specifies movement and direction and isn’t connected to an infinitive or phrasal verb.
1. Are in or to part of an infinitive or phrasal verb?
Yes: keep them separate.
No: Next question.
2. Are you answering a question of where, and/or specifying motion, movement, or direction?
Yes: keep them connected.
No: You likely don’t need either option and should figure out a new way to phrase your sentence.
In and to will be separate if either are a part of an infinitive or phrasal verb. If they are not part of verbs and are specifying motion, movement, or direction, they will be connected, forming into.
Write a sentence using both into and in to correctly. The thief quickly broke in to the safe and slipped the diamonds into his bag.