Definition: Bound Morphemes

Words and Word Parts

bound morphemes
The common prefixes im- and re- are bound morphemes, and so are the suffixes -s and -ous. These four bound morphemes are found (for example) in the words immoral, review, dogs, and dangerous,. Getty Images

A bound morpheme is a word element that cannot stand alone as a word, including both prefixes and suffixes. Free morphemes, on the other hand, can stand alone as a word and cannot be broken down further into other word elements.

Attaching a bound morpheme to a free morpheme, like adding the prefix "re-" to the verb "start," creates a new word or at least a new form of a word, like "restart." Represented in sound and writing by word segments called morphs, bound morphemes can further be broken down into two categories; derivational and inflectional morphemes.

Hundreds of bound morphemes exist in the English language, creating near-infinite possibilities for expanding unbound morphemes — commonly referred to as words — by merely attaching these elements to pre-existing words. 

Inflectional Versus Derivational Morphemes

The two classes of bound morphemes that linguists recognize to modify the grammatical class of words are inflectional and derivational morphemes. Inflectional morphemes predictably influence the base words to signal a change in quantity, person, gender, tense, or the like while leaving the base word's class unchanged.

Inflectional morphemes are considered more predictable because there are only eight in the closed set of accepted inflectional morphemes, which include the pluralizing "-s," the possessive "-'s," the third-person singular "-s," the regular past tense "-ed," the regular past participle "-ed," the present participle "-ing," the comparative "-er," and the superlative "-est." 

On the other hand, derivational morphemes are considered lexical because they influence the base word according to its grammatical and lexical class, resulting in a larger change to the base. Derivational morphemes include suffixes like "-ish," "-ous," and "-y" and prefixes like "un-," "im-" and "re-."

Andrea DeCapua describes this class of morphemes in her book "Grammar for Teachers" as having "to do with the vocabulary of language" wherein derivational morphemes "form an open set to which new words or word forms are frequently added." Oftentimes, these additions change the part of speech of the base word they're modifying, though that is not necessarily always the case, leading to derivational morphemes to be considered less predictable than their inflectional counterparts.

Forming Complex Words

Bound morphemes attach to free morphemes to form new words, oftentimes with new meanings. Essentially, there's no limit to the number of bound morphemes one can attach to a base word to make it a complex word. For instance, a misunderstanding is already a complex word formed from the base "understand" wherein "mis-" and "-ing" bound morphemes are added to change both the meaning of understanding ("mis-" means "not") and the verb tense ("-ing" makes the verb into a noun).

In the same way, you could continue to add more bound morphemes to the beginning of the word to make it even more complex and once again alter its meaning — though this has the potential to result in a convoluted word that's hard to understand. Such is the case with words like "antiestablishmentism," whose four bound morphemes change the original word "establish," which means "to form," into a word that now means "the belief that systemic structures of power are implicitly wrong."