Commonly confused words, and how to remember the difference
Affect or effect, which or that, fewer or less: the mix-ups editors fix most often.
Spellcheck will not catch these, because both words are real. Here are the pairs we correct most often.
| Pair | The difference | Remember it |
|---|---|---|
| affect / effect | Affect is usually a verb (to influence); effect is usually a noun (a result). | Affect is an action; effect is the end result. |
| which / that | That introduces information you need; which, after a comma, adds extra information. | Can you delete it without losing the meaning? Then it is which. |
| fewer / less | Fewer for things you count; less for amounts. | Fewer people, less time. |
| its / it's | It's means "it is" or "it has"; its belongs to it. | Try "it is". If it works, use it's. |
| complement / compliment | Complement completes; compliment praises. | Complement completes. |
| principal / principle | Principal means main (or a head teacher); principle is a rule or belief. | A principle is a rule. |
| ensure / insure | Ensure means make certain; insure is about insurance. | Insure is for insurance. |
| practice / practise | In UK English, practice is the noun and practise the verb. US English uses practice for both. | Like advice (noun) and advise (verb). |
| licence / license | In UK English, licence is the noun and license the verb. US English uses license for both. | The same rule as practice / practise. |
| stationary / stationery | Stationary means not moving; stationery is paper and pens. | Stationery includes envelopes. |
| i.e. / e.g. | i.e. means "that is"; e.g. means "for example". | E.g. gives an example. |
| comprise / compose | The whole comprises the parts; the parts compose the whole. | Avoid "comprised of"; write "consists of". |
A few that are not errors
- Splitting an infinitive ("to boldly go") is fine when it reads naturally.
- Ending a sentence with a preposition ("the people we worked with") is fine too.
- Starting a sentence with "And" or "But" is acceptable in most writing, though formal academic styles may prefer to avoid it.
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