Word Formation & Affixes
English builds many words by adding prefixes and suffixes to a base. At higher levels, recognising word formation helps you understand unfamiliar vocabulary and choose the correct form in formal and complex texts. The key is not simply knowing an affix but understanding how it changes meaning or word class.
- Level 2
- Level 3
Understand
Prefixes mainly change meaning
Prefixes are added before a base.
- un-: unclear, unreliable
- re-: reconsider, rebuild
- mis-: misunderstand, misrepresent
- over-: overestimate, overreact
- under-: underestimate, underfunded
Suffixes often change word class
Suffixes can turn one member of a word family into another.
- analyse → analysis → analytical → analytically
- rely → reliable → reliability
- signify → significant → significance → significantly
- persuade → persuasion → persuasive
Negative prefixes are not interchangeable
English uses several negative prefixes, including un-, in-, im-, ir-, il- and dis-.
The correct form depends on the word: inaccurate, impossible, irrelevant, illegal, dishonest.
Do not invent a negative form simply because a prefix exists.
Spelling can change
Word formation sometimes changes spelling.
Examples: decide → decision, explain → explanation, strong → strength.
A word family is related in meaning but not always mechanically predictable.
Word class must fit the sentence
Compare:
The result is significant. — adjective
The result has statistical significance. — noun
The result changed significantly. — adverb
The meaning is related, but grammar determines the form.
Example
Sentence: 'The evidence was not sufficiently ______ to support the conclusion.'
Base word: convince.
The blank follows was and is modified by sufficiently, so an adjective is needed.
Answer: convincing.
The task is solved by combining word family knowledge with sentence grammar.
How to do it
- Identify the base word.
- Decide what meaning needs to be added or changed.
- Use sentence grammar to decide the required word class.
- Choose a likely prefix or suffix.
- Check spelling changes.
- Read the complete sentence and confirm that both meaning and grammar fit.
- Record new vocabulary as a word family rather than as one isolated form.
Common mistakes
Mistake: This is a significance difference.
Better: This is a significant difference.
Mistake: unpossible.
Better: impossible.
Mistake: Assuming every base combines with every common suffix.
Better: Check real word-family patterns in context.
Mistake: Learning analysis but not analyse, analytical and analytically.
Better: Store related forms together.
Try it
Which form correctly completes the sentence? 'The researchers questioned the ______ of the measurement.'
- A. reliable
- B. reliably
- C. reliability
- D. rely
Answer: C. The structure 'the ___ of' requires a noun, and reliability is the noun form.
Key points
- Prefixes mainly add or change meaning.
- Suffixes often change word class.
- Negative prefixes follow established word patterns.
- Word formation can involve spelling changes.
- Grammar helps determine which member of a word family is needed.
- Learn words in families to expand vocabulary efficiently.
Related guides
Continue with a related guide.
Academic Vocabulary
Develop vocabulary that helps you express ideas clearly and precisely in formal and academic contexts.
Read the guideVocabulary in Context
Work out unfamiliar words by combining context, grammar, word parts and collocations instead of guessing from one clue.
Read the guideSynonyms & Precision
Choose words according to their exact meaning rather than treating similar words as interchangeable.
Read the guideNominalisation & Complex Noun Phrases
Understand how advanced formal writing packages information into noun phrases and when that makes writing more precise or more difficult to read.
Read the guide