Act up/ go off the rails

redgiant

Senior Member
Cantonese, Hong Kong
Hi, How to tell their differences?

If a child starts taking drugs, stealing money, running around with his gang, do you use "The child starts acting up"?

If a child starts locking himself up alone in his bedroom, refusing to eat and bath, acting like he's possessed by a demon, do you use "he starts going off the rails"?

Do "acting up" simply mean getting naughty and "going off the rails" imply a totally out of character behavior?

Behave badly or strangely
http://www.usingenglish.com/reference/phrasal-verbs/act+up.html

to start behaving strangely or in a way that is not acceptable to society
http://idioms.thefreedictionary.com/go+off+the+rails
 
  • ewie

    Senior Member
    English English
    Hullo RG. For me the emphasis of act up is on 'badly': 'behave in a way that the speaker doesn't approve of'; whereas for go off the rails the emphasis is on 'strangely': 'behave in a way that the speaker finds abnormal'.

    I've made this sound like a very clear-cut distinction. Of course, this being English, there isn't that: the two meanings shade into one another:(
     

    redgiant

    Senior Member
    Cantonese, Hong Kong
    Thanks ewie. Based on your explanations, if the speaker finds the child being crazy, insane, acting like a crook, It seems "go off the rails" is a better choice.
     

    ewie

    Senior Member
    English English
    Yes, I'd use go off the rails there. Another thing is that it sounds a lot more serious to me than act up.
     
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