Word formation: prefixes & suffixes
B2 47 / 50
In short
A prefix goes before a word and usually changes its meaning (happy -> unhappy); a suffix goes after a word and usually changes its part of speech (happy -> happiness -> happily). It is a learnable system, not a random list - and it is exactly what the FCE/CAE Use of English word-formation task tests.
The rule
Start from a base word and build a word family around it by adding parts:
- Prefix = meaning change, same word class: do -> redo, legal -> illegal.
- Suffix = often a new word class: verb -> noun (decide -> decision), adjective -> adverb (quick -> quickly).
Most B2 errors come from choosing the wrong word class for the gap. Read the sentence: does it need a noun, a verb, an adjective or an adverb? Then pick the suffix that produces that class. Watch out for the few families that build the new word on a relative of the base rather than on the base itself: strong -> strength -> strengthen, never strongen.
Negative prefixes make an opposite. Which one you use mostly has to be learned, but spelling follows the sound of the next letter:
| Prefix | Tendency / meaning | Example |
|---|---|---|
| un- | very common, “not” | happy -> unhappy, lock -> unlock |
| in- | ”not” (default) | correct -> incorrect, visible -> invisible |
| im- | before p, b, m | possible -> impossible, mature -> immature |
| il- | before l | legal -> illegal, logical -> illogical |
| ir- | before r | regular -> irregular, responsible -> irresponsible |
| dis- | ”not” / reverse | agree -> disagree, appear -> disappear |
| non- | ”not a”, usually hyphenated | non-smoker, non-fiction |
| mis- | ”wrongly / badly” | understand -> misunderstand, spell -> misspell |
Note that im-, il-, ir- are just in- reshaped to match the next sound.
Other useful prefixes:
| Prefix | Meaning | Example |
|---|---|---|
| re- | again / back | rewrite, reopen, return |
| over- | too much | overcook, oversleep, overpriced |
| under- | too little | undercook, underpaid, underestimate |
| pre- | before | preview, preheat, prewar |
| post- | after | post-war, postgraduate |
| anti- | against | antivirus, anti-social |
| ex- | former (hyphenated) | ex-wife, ex-president |
Forms & patterns
Noun suffixes (often from verbs or adjectives):
| Suffix | From | Example |
|---|---|---|
| -tion / -sion | verb | educate -> education, decide -> decision |
| -ment | verb | agree -> agreement, develop -> development |
| -ness | adjective | dark -> darkness, happy -> happiness |
| -ity | adjective | able -> ability, real -> reality |
| -er / -or / -ist | person who does it | teach -> teacher, act -> actor, science -> scientist |
| -ship | state / relationship | friend -> friendship, member -> membership |
| -hood | state / period | child -> childhood, neighbour -> neighbourhood; from an adjective: likely -> likelihood (not likelyhood) |
| -ance / -ence | verb / adjective | perform -> performance, different -> difference |
Adjective suffixes:
| Suffix | Meaning | Example |
|---|---|---|
| -ful | full of | care -> careful, use -> useful |
| -less | without | care -> careless, home -> homeless |
| -able / -ible | can be …ed | enjoy -> enjoyable, reverse -> reversible |
| -ous | having the quality | danger -> dangerous, fame -> famous |
| -ive | tending to | create -> creative, attract -> attractive |
| -al / -ical | relating to | nature -> natural, history -> historical |
| -y | full of | sun -> sunny, cloud -> cloudy |
Verb suffixes:
| Suffix | Meaning | Example |
|---|---|---|
| -ise / -ize | make / become | modern -> modernise, real -> realise |
| -en | make more (from short adjectives) | wide -> widen, short -> shorten; via the noun: strong -> strengthen, long -> lengthen |
| -ify | make | simple -> simplify, pure -> purify |
Adverbs: add -ly to the adjective: quick -> quickly, careful -> carefully. Spelling: happy -> happily (y -> i), gentle -> gently (drop -e), true -> truly; -ic adjectives take -ally: basic -> basically.
Word families - learn the whole set together, not single words:
| Base | Noun | Adjective | Adverb |
|---|---|---|---|
| happy | happiness | happy / unhappy | happily |
| decide | decision | decisive / indecisive | decisively |
| care | care / carer | careful / careless | carefully |
| photograph | photography / photographer | photographic | photographically |
Stress can shift when you add a suffix, so listen as well as spell:
- PHO-to-graph -> pho-TOG-ra-phy -> pho-to-GRAPH-ic
- Endings like -ity, -ion, -ic, -ical tend to pull stress to the syllable just before them: PUB-lic -> pub-LI-ci-ty, e-CON-o-my -> e-co-NOM-ic.
Examples
| English | Note |
|---|---|
| The instructions were unclear, so nobody knew what to do. | un- = “not”; opposite of clear. |
| It’s impossible to finish all this by Friday. | im- before p (not unpossible). |
| Parking here is illegal after six o’clock. | il- before l. |
| I completely disagree with that decision. | dis- reverses agree. |
| Sorry, I misread your message. | mis- = “wrongly”. |
| Her kindness surprised everyone in the office. | -ness turns the adjective kind into a noun. |
| They came up with a very creative solution. | -ive makes the adjective from create. |
| He answered every question nervously. | -ly makes the adverb (how he answered). |
Common mistakes
- unpossible -> impossible - use im- before p, b, m.
- He is a very success person. -> …a very successful person. - the slot needs an adjective, so add -ful.
- She speaks English very careful. -> …very carefully. - describing a verb needs the adverb -ly.
- His behaviour was unresponsible. -> …was irresponsible. - use ir- before r.
- We made a beautifull, carefull plan. -> …a beautiful, careful plan. - -ful has one l (two ls only when you add -ly: carefully).
Tips
- Decide the word class first. The gapped word in a Use of English task is almost always a different class from the word in brackets.
- The negative prefix is mostly fixed per word - when unsure, the spelling rule (im-/il-/ir- before p,b,m / l / r, in- elsewhere) at least keeps the form right.
- Learn words in families (decide -> decision -> decisive -> indecisive -> decisively); one base often gives you four or five exam answers.
- Watch the stress shift with -ity, -ion, -ic endings - the meaning may be obvious but the pronunciation moves.