A free morpheme and a bound morpheme

Every morpheme can be classified as either free or bound. These categories are mutually exclusive, and as such, a given morpheme will belong to exactly one of them.

Free morphemes can function independently as words (e. g. town, dog) and can appear with other lexemes (e. g. town hall, doghouse).

Bound morphemes appear only as parts of words, always in conjunction with a root and sometimes with other bound morphemes. For example, un - appears only accompanied by other morphemes to form a word.