Act up:

  1. If a machine or part of the body acts up, it does not work as it should
  2. To make somebody annoyed by behaving badly, trying to get attention, etc.

The kids started acting up.
The car's acting up again.

I would like to know how act up came to get its meaning. Also, what is the meaning of the word up and how is it being used? Is it compared with down in some way?

1 Answer 1


In phrasal verbs particle up can have various meanings and not necessarily express the opposite of down.

Up can express the happening, the emergence of something:

What's up ?
The kids started acting up.
I can't go on holiday, something unexpected's come up.
I'll pop up and see you on my way home.

In none of these cases could we obtain the opposite meaning of the phrase by replacing up with down as we can in get up/get down.
Or we'd have to change the verb altogether. For example we could say:

The kids are now calming down.

Up can mean other things as well. Apart from the opposite of down, one of its usual meaning is to express completion, such as in:

The car's paid up. I've no more debts.
Come on eat it up, finish what's in your plate.

It can express improving something :

Cheer up!
This text isn't very good, you should polish it up a little.


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