Why is the phrase run into and not run onto ?When you run onto someone you dont go inside his body(LOL).In is for anything with interior structure,at is for specific locations in time or in space and for every other thing we use on.So it should be run onto or bump onto someone because run in our particular case shows direction.

  • 1
    Impossible to answer - it's just one of those idioms you have to learn (run into = collide with or meet by chance). Oct 9, 2023 at 17:59

3 Answers 3


Yes, you can only use "in" when the thing has interior structure, when the subject is on the inside.

But "into" is a different preposition. It is defined thus by American Heritage Dictionary:

To the inside or interior of

So the primary preposition in the compound into is to rather than in.


He ran into the giant tortoise = He ran against the side of the giant tortoise, directed toward its center

He ran onto the giant tortoise = He ran to the top of the giant tortoise's shell, directed towards a space over the tortoise

  • into is just combined in and to .We are moving into your house , the house has a interior structure and move shows direction.
    – Cerise
    Oct 9, 2023 at 17:26
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    Yes, you can be in the house and not in the person. But into doesn't assert that you are in the target, merely directed toward the target's inside.
    – jrpear
    Oct 9, 2023 at 17:28
  • and I dont think on is for over something.Check this out:he is on the move ?What he is on top of the move ? no .
    – Cerise
    Oct 9, 2023 at 17:28
  • "But into doesn't assert that you are in the target, merely directed toward the target's inside".I dont think ur directed to the inside of someone when you run onto him , you are only directed to them(their skin or whatever).
    – Cerise
    Oct 9, 2023 at 17:33
  • "direction" is just a matter of which way you are oriented. You can be directed toward anything.
    – jrpear
    Oct 9, 2023 at 17:38

There is no specfic reason, this sense developed from earlier senses of into, and is now one of the secondary meanings of the word.

You could explore the sense development of "into" from a combination of the prepositions "in" and "to", to becoming an independent preposition with its own meaning, and that meaning expanding and generalising. It used to be a combination of "in" and "to" (900 years ago) but now it is a separate word from either. To investigate this development you would need a well-stocked library of Middle and Early Modern English

In particular at some point in the last 10 centuries, the word "into" acquired the sense of "(with verbs of motion) against (often suggesting movement with force)" So we have "crash into a tree" or "walk into a wall".

And from this sense, further development gives "have an unplanned meeting".

In English, as is every other language, words have meanings that can develop and change over time, and the word "into" has been developing for a long time.

Your error here is assuming that you can deduce every meaning of "into" from one of the senses of "in". That isn't possible.

  • If you do want to investigate the sense-development, then English Language & Usage is the right place to ask, since it is not an aspect of learning English, but learning about English.
    – James K
    Oct 9, 2023 at 20:53

By luck, in the phrasal verb "run into", the "into" part actually makes sense.

It has this meaning (from Merriam-Webster):

3 : to a position of contact with : against
ran into a wall

So, to "run into" someone means to "run to a position of contact" with them, in other words, collide with them while running.

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