Hadar Shemesh breaks down how to hear the difference between "can" and "can't" in spoken English. Unstressed "can" gets reduced to a quick sound, while "can't" keeps a fuller vowel and a t sound at the end, even if native speakers don't fully release it.
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This word is often reduced when it's unstressed in a sentence. It's not pronounced can as in yes, we can. In this case it's stressed. Usually it's pronounced as can I can do it. This word is never reduced, so even if it's unstressed in a sentence, it's always going to have the pure vowel in it. And here we have again the a as in cat that because of the n, actually changes to can. Can't. Now I really popped the t here, and that is perfectly fine. Can't. But you might struggle with hearing the difference, because sometimes native speakers might not pop the t. The t after an n at the end of a word is usually a held t and especially an after an n. It almost feels like you are just stopping the n abruptly. Listen. Can't, can't.