I sometimes have trouble with the preposition onto. Some of the time it’s pretty easy to know when I mean on to (two words), but other times I’m not so sure. The way most will explain it is if you can precede onto with the word up, then it’s one word: The dog jumped onto the table. That’s pretty clear. It implies a positioning on something. Here are some instances where you want two words:
• Hold on to my arm.
• Get on to the next part, please.
• Let’s move on to better things.
• Please hold on to this bag for me
But you do say:
• Hook the wire onto the nail
• They’re onto us (colloquial).
Into is a lot easier, but writers still mess it up. We say take into account, go into teaching, get into trouble, late into the night, run into a wall, look up into the sky. But you don’t want to “turn yourself into the police” because that would require a cool magic trick to transform yourself like that. And you don’t give into my demands because to “give in” is a verb-preposition combo structure. Just like you don’t fall into line. You “fall in” to line.
