The other day a writer emailed me and asked, “What is the difference between writing ‘into’ or ‘in to?’
You have to know the grammar police will notice this grandiose error every time. That’s not to say it’s not a common grammar faux pas, because it definitely is. So what is the difference and proper way to use each?
First thing we must realize is these prepositions are not interchangeable. "Into" has motion. "In" is a location or position. Once you get the hang of which one to use, you’ll see how easy it is.You should use ‘into’ when it's a question of location, for lack of a better word. "I went into the elevator," "I went into the field of nursing," "We practiced our song well into the morning," etc.
‘In to’ just happens sometimes. "I went in to buy some milk." In that sentence the ‘to’ is part of the infinitive ‘to buy.’
If you aren't sure which one to use, change the ‘in’ to ‘in order’ and see if it still works. "I went in order to the store" is wrong, but "I went in order to buy some milk" is right.
Note also that ‘into’ is unacceptable by English experts as slang. It’s weak, careless and vague. In proper English, it’s best not to use ‘into’ as someone being into something. An example: She's into herbalism. Instead, say, "She's a naturalist" or "She is interested in the health benefits of natural herbs."