Morphemes
Speakers of a language can recognize that word forms may include a number of units.
For example, we can make out that English word forms like plays, player, played and playing can be split into pieces; they are made up of one unit play, and a number of other elements like -s, -er, -ed and -ing.
All these elements are called morphemes, the minimal units of meaning or grammatical function that are used to form words (Lieber,
2009, p. 32).
Free and Bound Morphemes
From the examples given above, we can categorize morphemes into two broad classes: free morphemes and bound morphemes.
A free morpheme can stand alone as an independent, single word, for example open and visit. In contrast, a bound morpheme cannot normally stand alone and must be typically attached to another form.
For example, the plural morpheme -s can only occur when it is attached to nouns, or the past tense -ed morpheme must be attached to verbs. Thus, we can state that all affixes in English are bound morphemes, including prefixes attached to the beginning of another morpheme (such as re- in words like reinvent, reopen and rewrite), and suffixes attached to the end of another morpheme (such as -er/-or in words like opener, inventor and writer).
Some bound morphemes (e.g. cran-) are called “bound base morphemes” and they are not meaningful in isolation but have meaning when combined with other morphemes. For example, cran- must occur with berry (cranberry, huckleberry) and more recently with apple, grape, or some other fruit (cranapple, crangrape, crananidin).
Finally, the morpheme to which we attach an affix is called the base or stem morpheme, and it may be free like dog (both a free morpheme and a free base) or bound (like -s or cran-).