Definition: Bound Morphemes

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

Attaching a bound morpheme to a free morpheme, such as by adding the prefix "re-" to the verb "start," creates a new word or at least a new form of a word, in this case, "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 attaching these elements to preexisting words. 

Inflectional vs. Derivational Morphemes

Inflectional morphemes influence the base words to signal a change in quantity, person, gender, or tense 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." 

By contrast, 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," as well as prefixes like "un-," "im-," and "re-."

Often, these additions change the part of speech of the base word they're modifying—though that is not necessarily always the case—which is why derivational morphemes are considered less predictable than inflectional morphemes.

Forming Complex Words

Bound morphemes attach to free morphemes to form new words, often with new meanings. Essentially, there's no limit to the number of bound morphemes you can attach to a base word to make a more complex word. For instance, "misunderstanding" is already a complex word formed from the base "understand," wherein "mis-" and "-ing" are bound morphemes that 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."