Is it acceptable to use "not polite" instead of "impolite"?

And generally speaking about other words in their negative form? By adding a prefix only? Can I use "not + the positive form" instead?

For example:

It's incorrect. > It's not correct.

It's impossible > It's not possible.

It's irreversible > It's not reversible

It's unbelievable > It's not believable.

It's imperfect > It's not perfect.

Are both sentences valid or acceptable?

  • There are times when any of these might be used, but I am not going to provide contexts for all of them.
    – Lambie
    Commented May 21, 2018 at 12:49

1 Answer 1


The best time to use the not + positive form is when you are trying to emphasize what it’s not.

Today, the normally trivial task was impossible.

Today, the normally trivial task was not possible.

Be careful, the damage caused is irreversible.

Be careful, the damage caused is not reversible.

This is not the only case it's used, but probably the most common.

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