What is the opposite of not?

Answer 1

The opposite of not (as a negative) is simply the omission of the word. The opposite of "not something" is usually "is something" -- with the possible addition of modifiers such as definitely or indeed.

Or, otherwise stated, the opposite of not is "is."

When someone says, "No, it's not" the opposite is "Yes, it is."

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Another opinion:

I'd like to suggest there is not an opposite for not.

I am not certain of this. Not indicates a condition attached to certain words or concepts, without necessarily implying what remains after application of the not. There is no word that can always be put in its place to indicate the opposite meaning. [as in He is tall; he is short. The food is delicious; the food is awful.] You cannot even reliably remove the word not in order to get the opposite meaning. Consider these examples:

She is not obnoxious.

Not one soldier backed down.

Not only is it sunny; it is also warm and breezy.

I prefer chocolate, not strawberry.

You can take not out of the first sentence, but not the others. The opposite of not one soldier isn't "one soldier". It would be an indefinite number, one or more soldiers, or some soldiers. While "strawberry" seems certainly to be the opposite of "not strawberry", the fourth sentence demonstrates this might not always be true. I'm not even sure that we could say the opposite of the fourth sentence is "I prefer strawberry, not chocolate." How is that "opposite"? What if my preference is lemon, but it is not being offered?

It seems that not is a passive function; an exclusion from any number of alternatives. Without further qualification, "not butterfly" could mean literally anything else, including the null set. An active option isolates a specific object or category to the exclusion of everything else.