Small/Large Little/Big

Even though English is my native language, I've never understood this question: why is it that in English:

small is the opposite of large
little is the opposite of big
small and little are synonyms
large and big are synonyms

However,

small is NOT the exact opposite of big
little is NOT the exact opposite of large

?

I don't know why either. It does seem a little strange.

''It does seem a little strange.''

No pun was intended with that sentence.

I think it seems a small strange. ; )

I wouldn't be quite sure about that completely, as it seems like that, at least here, "small" can serve as a direct opposite with both "large" and "big", whereas "little" seems to not be an exact opposite of either "big" *or* large. If anything, "small" seems to indicate just literal low size with respect to the given scale, whereas "little" seems to have a diminuitive aspect beyond expressing simply a low size. As for "large", it expresses just literally large size with respect to the given scale, whereas "big" can express this alone, but may *also* express some sort of antidiminuitiveness beyond such a literal indication of size alone. However, this kind of aspect is not as strong with "big" as it is with "little", and hence it can still be paired with "small" in comparisons and like nonetheless.

There are certain cases where substituting ''little'' and ''big'' for ''small'' and ''large'' wouldn't sound right.

For example, the sentence ''They have small, medium and large shirts at the clothing store.''

To say that as:

''They have little, medium and big shirts at the clothing store'' would sound strange.

Same with:

''They have little, medium and large shirts at the clothing store''

or

''They have small, medium and big shirts at the clothing store''

Thus they are not completely synonyms.