In to vs. Into, On to vs. Onto: All About the Verb

Carla writes:

Hi Snarky! Would you please run through when to use in to and when to use into? I also mix up on to and onto. Thank you!

Sure thing, Carla. This question tends to crop up only when we're writing, since both options sound identical in spoken English. Sometimes it's about the preposition. But more often, it's about the verb.

Quick rules:

• There should generally be only one preposition per phrase. 
• Use the prepositions into and onto to indicate movement from one place to another. I stepped into the room. He stepped onto the podium. She jumped into the pool. I tossed my book onto the desk.
• You can often use into and onto interchangeably with in and on, which are also prepositions. She jumped in the pool. I tossed my book on the desk. In both sentences, the sense of movement is obvious through context.
• If the preposition is an integral part of a phrasal verb, also known as a two-word verb*, then don't consider it a preposition; consider it part of the verb. Keep phrasal verbs intact.
  
  
  
  1. Correct: The robbers will break in to the bank at 6pm. The phrasal verb is 'break in,' meaning to enter without permission. In is part of the verb and the preposition is to.
     Incorrect: The robbers will break into the bank at 6pm. The phrasal verb has been corrupted.
  2. Correct: I'll look into this matter before the end of the day. The phrasal verb 'to look into' means to investigate.
     Incorrect: I'll look in to this matter before the end of the day. The back-to-back prepositions in this phrase signals the error.
  3. Correct: Turn your paper in to your teacher. The phrasal verb 'to turn in' means to submit. In is part of the verb and to is the preposition.
     Even better: Turn in your paper to your teacher. The phrasal verb is kept together.
     Incorrect: Turn your paper into your teacher. Shazam! Your paper is now your teacher. 'To turn into' is another phrasal verb meaning to transform. D'oh, that's not what you meant.
  4. Correct: I am really into alternative music. The phrasal verb 'to be into' means to be passionate about.
     Incorrrect: I am really in to alternative music. The double preposition is the clue that there is an error.