This is often a problem for native speakers also! I can tell. / I can't tell. ~~sound basically identical And incredibly, sometimes even things like I can help /// I can't help ~sound almost identical, depending on the accent / individual's speaking style! Context clues can help, for example someone shaking their head from side to side (negative) or nodding (positive), but this is harder on the phone when you can't see the person. Sometimes a little bit of logic can help, for example if I ask someone if they can tell what is written on a sign...and they say "I can-t-ell."...probably they said "I can't tell.", because if they knew what was on the sign they would tell me that information. But ultimately, it is a completely understandable issue, so don't feel bad about it, and you do not need to be shy about asking people to repeat themselves or clarify! I always tell my students members of my native-speaking family ask "Can? Or can't?" all the time, so you shouldn't worry about doing it!

Good question! Native English speakers will speak very fast! I would suggest asking to person “ did you say can or can not?”. Be confident to ask people to repeat. We do it too!

One way to hear it, Even if the person is mumbling, is that "can't" will always take longer to say. You can hear the small amount of extra effort when a person says "can't". Also, when people mumble "can", they often connect it to the next word. But it is not possible to do this with "can't" So if you can hear a small space between the 2 words, that is a clue.

Honestly, as a native English speaker from the US, don't worry! We often misunderstand each other when it comes to can and can't! A: 'I ca@#% come to the party tonight.' B: 'What'd you say? You caN? Or you caN'T?' A: 'I caN'T come!'

This came up before. In my opinion (at least in US English) CAN tends to continue in the flow of the sentence, whereas CAN"T has an abrupt stop at the end. So, if you can hear a brief silence after the word it's usually CAN'T; if not, it's usually CAN. Examples: I CAN DO THAT sounds like ICANDOTHAT I CAN'T DO THAT sounds like ICAN DOTHAT