Hi!
Sometimes I have trouble with the sound “can” and “can’t” when I am listening. It sounds equal to me, but of course, it changes totally the meaning of the sentence.
Is there some way to catch the right meaning when you are listening?
Even native speakers often have to ask for clarification. You have to judge by the context and when speaking I often make sure I say “can not” to avoid confusion.
Thank you Steve!
Yes, using “can not” is an option, however once I read that it is a bit old-fashioned, but I’m not sure.
“can’t” is often the most highly stressed word in a phrase while “can” is often unstressed
Hi Oscar
The way to differentiate between these two words is knowing that the stress is almost never on ‘can’ (it’s on the verb that follows), whereas it’s always on ‘can’t’.
It’s so crazy that you asked this because I just happened to randomly click on this advertisement for improving your English pronunciation on the side of my Google Mail account and this article about can vs. can’t is what popped up (though I already knew about this difference from explaining it to my students in Spain):
http://www.pronunciationpatterns.com/accent_tips.php?gclid=CJn_ponVtZ4CFQ4NDQod0GEPlg
Thanks Dooo and David for your responses!
I CAN say that your posts CAN’T be more useful 
I beg to disagree with the two previous posters. -
If “can’t”, (or “can”) is stressed, things are easier. But that is not always the case.
In fact “can’t” is often not stressed. I can’t tell you how many times I have heard it not stressed. Sometimes there are expressions that give it away, even if it is not stressed although I can’t seem to remember them all. You can’t really make a mistake with these, if you are used to them so I can’t give you any better advice than to keep getting more and more familiar with the language, don’t sweat it when you do not understand, don’t hesitate to ask for clarification, and use cannot more often when you speak. That is what I do.
Thanks again Steve for your time.
The difference between ‘can’ and ‘can’t’ is obvious if it’s British English (two different vowel sounds: /kæn/ and /kɑnt/), but if it’s another kind of English (American/Canadian/Irish/Scottish/Australian…New Zeeland…Indian?) the vowel sounds are roughly the same. (/kæn/ and /kænt/)
I perceieve ‘can’t’ as slightly longer (stressed or not), while ‘can’ is somewhat long only when stressed (if unstressed, I hear it as /kən/). To my non-native ears.
Does this make sense?
I actually agree with Steve in general. The answer is to just get used to the language. I would argue that there is a general tendency to stress ‘can’t’ and not “can”
try this exercise, just for fun. it is natural sounding spoken sentences with “can” or “can’t” you have to guess which one
In Australia (and I believe UK as well), the two don’t sound similar. “Can” sounds similar to what it does in North America (rhyming with man, tan, fan etc) but “Can’t” rhymes with “aunt” (in Australia, not in North America) and “blunt” (but it’s a bit longer, like “art”). In fact, here, ‘can’t’ sounds very similar to a particularly rude word in English. Hope that helps.
In the southern U.S. (presumably through out the entire country, too, but I’m not sure) people generally do not pronounce the ‘t’ in can’t when speaking quickly. It comes out like can with a little stop at the end.