Word Formation: Building Words with Prefixes and Suffixes
How to turn one English word into five — the prefix and suffix patterns that exams test directly and that multiply your vocabulary.
Learning decide teaches you one word. Learning how English builds on it teaches you five: decide, decision, decisive, decisively, indecisive. This is the highest-leverage vocabulary work at B2, and exams test it directly with gapped-word tasks.
Suffixes tell you the word class
Nouns: -tion, -sion, -ment, -ness, -ity, -ance/-ence, -ship, -hood
inform → information, agree → agreement, happy → happiness, able → ability
People: -er, -or, -ist, -ian, -ant
employ → employer / employee, science → scientist
Adjectives: -able, -ible, -ful, -less, -ous, -ive, -al, -ic, -y
care → careful / careless, danger → dangerous, create → creative
Verbs: -ise/-ize, -ify, -en
modern → modernise, simple → simplify, wide → widen
Adverbs: -ly
careful → carefully
If a gap follows a/an/the it wants a noun; before a noun it wants an adjective; modifying a verb it wants an adverb. Read the slot first.
Negative prefixes
| Prefix | Typical use | Example |
|---|---|---|
| un- | most common | unhappy, unable, unlikely |
| in- | Latin-origin words | incorrect, invisible |
| im- | before m, p | impossible, impatient |
| il- | before l | illegal, illogical |
| ir- | before r | irregular, irrelevant |
| dis- | verbs and some adjectives | disagree, dishonest |
| mis- | wrongly | misunderstand, misuse |
The im- / il- / ir- rule is purely about the following letter, so it is one of the few genuinely reliable spelling rules in English.
Other useful prefixes
re- again (rewrite) · over- too much (overestimate) · under- too little (underpaid) · pre- before (preview) · co- together (cooperate) · anti- against (antisocial)
Watch the stress and spelling
Adding a suffix often moves the stress:
PHOtograph → phoTOgrapher → photoGRAPHic
And frequently changes the spelling:
happy → happiness (y → i) · able → ability · decide → decision
Two traps
Not every -ly word is an adverb: friendly, likely, lonely and lovely are adjectives.
Some negatives are not opposites: invaluable means extremely valuable, not worthless. Flammable and inflammable mean the same thing.
Test yourself
The quiz below gives you a root word and a slot. Decide the word class first, then the form.