The difference between Certain and Impossible

When used as nouns, certain means something certain, whereas impossible means an impossibility.

When used as adjectives, certain means sure, positive, not doubting, whereas impossible means not possible.

Certain is also determiner with the meaning: having been determined but not specified.

Certain is also pronoun with the meaning: unnamed or undescribed members (of).

check bellow for the other definitions of Certain and Impossible

Certain as an adjective:

Sure, positive, not doubting.

Examples:

"I was certain of my decision."
Certain as an adjective (obsolete):

Determined; resolved.
Certain as an adjective:

Not to be doubted or denied; established as a fact.
Certain as an adjective:

Actually existing; sure to happen; inevitable.

Examples:

"Bankruptcy is the certain outcome of your constant gambling and lending."
Certain as an adjective:

Unfailing; infallible.
Certain as an adjective:

Fixed or stated; regular; determinate.
Certain as an adjective:

Not specifically named; indeterminate; indefinite; one or some; sometimes used independently as a noun, and meaning certain persons; see also "one".

Certain as a pronoun (with ''of''):

Unnamed or undescribed members (of).

Examples:

"There where serious objections to certain of the proposals."

Impossible as an adjective:

Not possible; not able to be done or happen.

Examples:

"It is difficult, if not impossible, to memorize 20,000 consecutive numbers."

"Sarah thinks that nothing is impossible because things can always somehow happen."
Impossible as an adjective (colloquial, of a person):

Very difficult to deal with.

Examples:

"You never listen to a word I say – you're impossible!"
Impossible as an adjective (math, dated):

imaginary

Examples:

"impossible quantities, or imaginary numbers"