Contraction

A contraction in English is the shortening of a word. In place of the missing letter or letters, an apostrophe ( or  ) is placed.

Contractions are very common but are considered informal.

Types of contractions
Common contractions include but are not limited to "don't" ("do not"), "isn't" ("is not"), and "aren't" ("are not").

Nouns can be contracted as well; e.g., "This cake'll be good" (This cake will be good).

Some uncommon contractions (which are grammatically correct but are rarely used) include but are not limited to "needn't" ("need not"), "mustn't" ("must not"), and "amn't" ("am not").

Contractions are not always just two words combined. Long contractions include but are not limited to "couldn't've" ("could not have"), "wouldn't've" ("would not have"), and "I'dn't've" ("I would not have"). These are considered very informal but are grammatically correct.

Words can be contracted to the point where they start or end with an apostrophe, too. Some examples are: "'em" ("them") and "o'" ("of").

"Aren't I?"
Sentences ending with "aren't I" are acceptable, despite "are not I" not being grammatically correct. This is because "amn't I" ("am I not") is considered awkward to spell and pronounce, and it is a regional contraction, limited to Scottish and Irish.