I was proof-reading one of my manuscripts recently, and it occurred to me how often I use “in to” when I mean “into”.
Grammatically speaking, ‘into’ is a preposition which often answers the question “where?”. For example, Kim and Tim went into the office only to realise they were in the wrong building.”
But sometimes ‘in’ and ‘to’ just find themselves next to one another in a sentence. “Fred jumped in to rescue his dog.” Of course, that wouldn’t be the case had we said, “Fred jumped into the river to rescue his dog.”
The best tip I have seen is to leave a pause between ‘in’ and ‘to’, saying it aloud. If it sounds wrong, chances are you need ‘into’.