Every morpheme can be classified as either free or bound.[3]
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. Most bound morphemes in English are affixes, particularly prefixes and suffixes, examples of suffixes are: tion, ation, ible, ing, etc. Bound morphemes that are not affixes are called cranberry morphemes.
Words can be put together to build larger elements of language, such as phrases (a red rock), clauses (I threw a rock), and sentences (He threw a rock too, but he missed).