Language is often inefficient. Even in the most common and used phrases, often the negative and positive can sound very similar, making it difficult to understand the meaning sometimes unless you understand the context. For example, in French:
C’est plus propre – It’s cleaner (more clean)
Ce n’est plus propre – It’s no longer clean
BUT also it’s common to omit the n’ when speaking quickly so in effect the second sentence can sound identical to the first sentence – and they are pretty much opposite in meaning!
I can do it
I can’t do it. (In standard English we hear the difference in vowel sound in “can” and “can’t”)
But there’s often a problem when someone’s accent doesn’t differentiate between the two vowels. Because there are many second language speakers now of English through business, tourism and migration, it’s getting harder to hear this difference in vowels. There are possibly some native speakers with different accents who also pronounce these two words similarly – and it’s common for the final “t” to be almost silent.
There are other examples, will think!
But just to say, when opposites in a language sound very similar, that’s not very logical, is it?