Prefixes  

Prefixes are morphemes (specific groups of letters with particular semantic meaning) that are added onto the beginning of roots and base words to change their meaning. Prefixes are one of the two predominant kinds of affixes—the other kind is suffixes, which come at the end of a root word.

Unlike suffixes, which can be either inflectional (changing only the grammatical function of a word without changing its basic meaning) or derivational (creating a word with an entirely new meaning), prefixes can only be derivational; adding a prefix always changes the basic meaning of the word.

In this section, we'll look at some of the most commonly used prefixes, but first let’s look at some conventions regarding how they’re used.

Prefixes generally do not affect the spelling of the root word to which they are attached: they are simply placed immediately before the word without a space (although some, as we’ll discuss later, may be attached with a hyphen).

However, while a root word’s spelling does not change with a prefix, we do sometimes have to alter the prefix itself depending on the spelling of the word it precedes. For example, the prefix a- becomes an- when coming before a vowel; the prefix in-, meanwhile, can change to ig- (before n-), il- (before l-), im- (before b-, m-, or p-), or ir- (before r-).

In addition, many prefixes are only able (or only tend) to attach to certain parts of speech. For example, the prefix un- (meaning “not”) generally only attaches to adjectives, as in unhappy or uncomfortable; when un- means “to do the opposite of,” it only attaches to verbs, as in uncork or unlock. Attaching un- to a root noun, on the other hand, is usually not done. For instance, undesk or unsky are incorrect. While technically correct words, unhuman and unbelief are not very common; we would more usually write nonhuman and disbelief.

Many prefixes will attach to both existing English base words as well as roots derived from foreign stems (parts of longer words used to form combinations), most often Latin or Greek.

When we look at examples of common prefixes further on, we’ll distinguish when prefixes attach to existing English words (adjectives, nouns, or verbs), Latin and/or Greek roots, or both. Note that some guides may call prefixes that attach to foreign-language roots “combining forms” rather than prefixes, a distinction that we’ll touch upon next.

When defining different prefixes, a distinction is sometimes made between “true” prefixes and “combining forms” of words. The precise definition of one compared to the other is not often clear, and, depending on the source, the distinction between the two is often inconsistent or contradictory.

The simplest explanation tends to be that a prefix can only attach to a base word (an English word that can be used on its own without a prefix or suffix), while a combining form is an adaptation of a larger word (typically Greek or Latin) that only attaches to another combining form (meaning neither element cannot stand on its own as an independent word).

What complicates this distinction is the fact that a morpheme could be considered a prefix in one instance and a combining form in another. For example, auto-, meaning “of or by the same person or thing,” functions like a “true” prefix in the word autoimmune, but it is usually considered a combining form, as in the word autonomy. Likewise, ex- as a prefix meaning “former” (as in ex-boyfriend) is sometimes contrasted with ex- as a combining form meaning “out” (as in exclude), yet the morpheme is more often considered a prefix in both cases by most dictionaries.

In reality, prefixes and combining forms behave the same way and essentially perform the same function in a word, so there’s no real benefit in dividing them into two separate categories. Doing so simply adds an unnecessary complication, especially for those learning the fundamentals of the language. As such, the list of common prefixes we’ll look at next makes no distinction between prefixes and combining forms—it’s more important to understand the different meanings they can have so that we can see a pattern in the way words are formed and spelled.

In the table below, we’ll look at different prefixes that commonly appear in English, noting their various meanings, the parts of speech they most typically attach to, and several example words in which they appear.

It’s important to note that this is by no means a complete list; there are far too many to include here. Rather, it is intended to give you an idea of how prefixes are used and how they may affect the meaning and spelling of words we use every day.

As you can see from the examples we’ve looked at, the vast majority of prefixes don’t require a hyphen when they are attached to a root. However, it is sometimes the case that adding a prefix to a stem can result in a word that is difficult or confusing to read, or else results in a spelling that overlaps with an existing word. In these cases, we can use a hyphen between the prefix and the stem word to clarify the meaning of the new word.

Many writers choose to add a hyphen when the last letter of the prefix and the first letter of the root are both vowels (especially when they are the same letter) so as to avoid creating a word that is difficult or confusing to read. For example:

Note that this hyphen is almost always optional and up to the writer’s discretion, and many double-vowel prefixed words are now commonly spelled without the hyphen (especially in American English). If in doubt, you can probably omit the hyphen, but use a good dictionary or check your school’s or business’s style guide to be sure.

Another instance when we might use a hyphen is when the resulting spelling would be confusing or awkward to read. For example:

Again, using the prefix without a hyphen is often a correct way to spell the word as well, so the hyphen is purely up to the writer’s discretion.

When adding a prefix (especially de- and re-) creates a word that looks the same as (or similar to) an existing word with a different meaning, we should use a hyphen to avoid confusion. For example:

When a prefix is paired with a proper noun or a proper adjective, we use a hyphen so we don’t have a capital letter appearing in the middle of a word. While hyphens have been almost always optional in our previous examples, we always use a hyphen with proper words. For example:

Note that some style guides suggest using an en dash ( – ) instead of a hyphen when a prefix is used with a proper noun or adjective that is already a compound, as in the second example. Using this method, it would look like this:

However, this is entirely a personal preference, unless the style guide used by your school or employer specifically prescribes its use.

In addition to proper nouns and adjectives, we almost always use a hyphen with the prefixes self- and ex- (when it means “former”), as in: