A request has come in from a reader to write about distinguishing between “can”, “may” and “might” – so here goes. Again, my sources of reference have been the Oxford English Dictionary, New Hart’s Rules and the New Oxford Dictionary for Writers and Editors.
Can vs. May
Can implies the ability to do something. “Can she play the piano?” – is she able to, at any point in time, play the piano? Is she capable of it? Has she learnt to play it?
May implies permission to do something or the possibility of doing something. The latter is probably the easy one – “She may play the piano if she feels up to it” introduces the possibility of her doing so. “May she play the piano? ” is asking for permission to do so.
An amusing way to remember this – “May I play this piano?” – “Of course you may. But CAN you play the piano?” – “No, I never learnt to do so!”
You do also find this one in discussions with parents and teachers. “Can I leave the table?” – “You are certainly ABLE to leave the table, but whether you have permission is a different matter!”
May vs. Might
I admit here that I had to do some research on this one. Traditionally, may is used in the present/future tense, and might in the past tense. So: “I may have some coffee after dinner if I’m still thirsty” vs. “He might have known his attacker.”
All clear? Oh, and while we’re on cans and mays … “cannot” is preferably used as one word, rather than “can not”. The only exception is in constructions like “He can not only do this, but also the other.”
LibroEditing proofreading, editing, transcription, localisation 
notjustlaura
May 10, 2011 at 3:55 pm
Your ‘leave the table’ example brings back memories!
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libroediting
May 12, 2011 at 5:10 pm
Ha – I thought it would for some people!
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Jen
May 10, 2011 at 5:28 pm
Interesting, thanks – I think I knew all that in theory but whether I do it right in practice is another question!
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Jen
May 10, 2011 at 5:32 pm
And I just used an adjective there instead of an adverb, I know!
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libroediting
May 12, 2011 at 5:09 pm
The shame, the shame!
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libroediting
May 12, 2011 at 5:10 pm
Glad people are finding this stuff interesting!
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Ali
May 12, 2011 at 5:01 pm
Excellent – I think I knew all that without knowing I knew it : ) grammer was badly if ever taught to my generation at school I find – well in state B’ham schools anyway. However I am pretty sure I get it wrong all the time – as when I write things – especially online – I rarely proof read or spell check before sending – lazyness I suppose.
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libroediting
May 12, 2011 at 5:09 pm
I didn’t know the official rule about “might” till I looked it up, I have to admit! I think it’s more relaxed now. I learnt more grammar doing Latin and French and then studying the English language at University than I did at school …
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