Idiomatic combinations and easily confused words
Choose conventional word combinations and distinguish words whose similar forms conceal different meanings.
What you will tackle
- Use conventional verb/preposition combinations
- Distinguish affect/effect, then/than and principal/principle
- Choose words by meaning in context
- Revise without changing the intended claim
Usage includes conventional combinations
In standard edited English, a result may depend on a condition, differ from another result, contribute to an outcome or comply with a rule. A researcher may be responsible for a measurement and capable of repeating it. These combinations are idiomatic: translating a preposition literally from another language may not produce standard usage.
Meaning decides the word
Affect commonly means influence, while effect commonly names a result; ‘effect change’ is the less common verb meaning bring it about. Than introduces a comparison; then can mark sequence. A principle is a rule or belief; principal can mean main or a school leader. Their indicates possession, there a place or existence, and they're means they are. Do not choose a word merely because it sounds similar.
Build your notes, then practise
Work on paper before opening an explanation. Guided tasks provide a starting point; independent tasks remove the scaffolding; application tasks ask you to justify a method or interpretation in context.
Guided practice
Guided 1
Correct the prepositions: ‘The result depends of temperature, differs to the control, and contributes for the discussion.’ Choose affect/effect: ‘Heat may __ the reading; that __ must be measured.’
Show a starting hint
Decide whether each blank names a thing or performs an action.
Compare with the explained answer
- The conventional combinations are depends on, differs from and contributes to.
- The first blank needs the verb affect, meaning influence.
- The second needs the noun effect, meaning result.
Answer / response criteria: on; from; to; affect; effect.
Independent practice
Independent 1
Choose: ‘First compare the trials, then/than calculate the mean.’ ‘The principal/principle reason was cost.’ ‘They're/Their results differ, and there/their is no confirmed cause.’ Correct ‘capable to repeating the trial’.
Compare with the explained answer
- Sequence takes then; the main reason is the principal reason.
- Possession takes their results; existence takes there is.
- The conventional expression is ‘capable of repeating the trial’.
Answer / response criteria: then; principal; Their; there; capable of repeating.
Application practice
Application 1
Revise: ‘The team complied to the safety rule. Their prepared to effect the measurement, but no affect was recorded.’ Preserve that they followed the rule and were ready to influence a reading, although no resulting change was observed.
Compare with the explained answer
- Use ‘complied with’ for following a rule.
- Use ‘They're prepared to affect the measurement’ for they are ready to influence it.
- Use noun effect for the observed result: ‘but no effect was recorded’. A clearer complete revision can use ‘were prepared’ to preserve a past narrative.
Answer / response criteria: ‘The team complied with the safety rule. They were prepared to affect the measurement, but no effect was recorded.’
What can you explain now?
Revise: ‘The team complied to the safety rule. Their prepared to effect the measurement, but no affect was recorded.’ Preserve that they followed the rule and were ready to influence a reading, although no resulting change was observed.
Compare with the explanation
‘The team complied with the safety rule. They were prepared to affect the measurement, but no effect was recorded.’
Explain the reasoning before comparing. This review records your self-assessment rather than an official score or mastery decision.
After trying it yourself, choose your next review. This is your self-assessment.
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Source and review status
Coverage follows the named requirements and examples in the 2026–2027 ACT test guide and subject descriptions. That guide explicitly does not list every possible topic. The broader coded College and Career Readiness Standards are also mapped to conceptual teaching and practice; this does not calibrate a learner to a score band. The separate scientific-background context list and reading-complexity rubric have their own stated limits.
Original teaching and explained self-check practice are available. Specialist review and difficulty calibration remain pending. Essays require self-check or teacher review and are not automatically marked or awarded official scores.
Official source specification / guide