If I were the security guard, could I just say, "You can't do this!"


1 Answer 1


Yes you can say either. There is actually a difference between cannot do and cannot be doing, the latter is like a juxtaposition - it uses be + ing and this usually is used for an ongoing action, for example if someone was graffitiing on some walls, then the security guard shouts: “You cannot be doing this!” and the person graffitiing on the wall says “Well I am and I can”.


What the security guard is saying is like an oxymoron, when he says “You cannot be doing this” “cannot” in this case is not a certain probability of not being able to; (related can not vs must not?) rather it is more like “should not” than “cannot”. Because they are able to do it, it is just frowned upon and illegal. I do not know if this usage of “cannot” is idiomatic... but there is certainly nothing wrong with that sentence. “You must not be doing this!”is a bit too formal and “You should not be doing this!”-hypercorrect (sorry!).

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .