Commonly confused words
Forty-five word pairs that spell-checkers wave through and readers notice anyway, with plain-English meanings, wrong-vs-right examples and a memory trick for each of the worst offenders.
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Commonly confused words are pairs (and trios) that sound alike or look alike but mean different things. They are the most forgiving kind of error for a spell-checker and the least forgiving for a reader: every word on this page is spelled correctly, so software usually stays quiet, while a hiring manager or a client notices your for you're instantly.
The good news is that the list is short. A few dozen pairs account for most real-world mix-ups, and nearly every one has a one-line test. Start with the eight heavy hitters below, then use the full table as a reference.
The eight pairs that cause the most trouble#
Affect vs effect#
In everyday use, affect is the verb (to influence) and effect is the noun (the result). The American Heritage Dictionary usage note adds the two wrinkles that trip up careful writers: effect is also a verb meaning "to bring about" (to effect a cure), and affect is a rare noun in psychology meaning an emotion. Cambridge's grammar guide gives the same core split.
The new policy will effect everyone's schedule, but nobody knows the affect yet.
The new policy will affect everyone's schedule, but nobody knows the effect yet.
Verb that means "influence" = affect. The thing that results = effect.
Their vs there vs they're#
Their shows possession, there points to a place or introduces a statement (there is), and they're is the contraction of they are. Cambridge notes they are pronounced the same, which is exactly why fingers type the wrong one at speed.
Their going to leave they're bags over their.
They're going to leave their bags over there.
Test: if "they are" fits, write they're. "There" hides the word "here," a place.
Its vs it's#
It's always means it is or it has. Its is the possessive, and like his and hers it takes no apostrophe (Cambridge). This one feels backwards because we normally add 's to show possession, but possessive pronouns never use an apostrophe.
The company changed it's logo because its been ten years.
The company changed its logo because it's been ten years.
Then vs than#
Than compares (taller than); then is about time or sequence (first this, then that). A related nuance from the American Heritage usage note on "then": She took a slice of pie, then left is widely accepted, and when then joins two actions like that, a comma usually goes before it.
This laptop is faster then my old one.
This laptop is faster than my old one.
Lose vs loose#
Lose (one o, rhymes with choose) means to misplace or fail to win. Loose (two os, rhymes with goose) means not tight. The extra o is the problem: people add it when they mean lose.
Don't loose your keys.
Don't lose your keys; the ring is loose.
Loose has room to spare, like its extra o.
Compliment vs complement#
A compliment is praise. A complement completes or perfects something. The American Heritage note points out that the two are "quite distinct in meaning" and confused only because they sound the same.
The sauce is a nice compliment to the fish.
The sauce is a nice complement to the fish, and the chef got a compliment.
Complement completes. Compliment: "I like you."
Principal vs principle#
Principle is only ever a noun: a rule, belief or standard. Principal is a noun (the head of a school, a main party in a deal, or the original sum of a loan) and an adjective meaning "chief." According to the American Heritage usage note, the two "have no meanings in common."
The principle reason I refused was a matter of principal.
The principal reason I refused was a matter of principle.
Fewer vs less#
The traditional rule: fewer for things you count, less for amounts you measure. The American Heritage Usage Panel largely backs it; in its 2006 survey only five percent accepted There are less crowds at the mall these days. But the same note lists solid exceptions: less than three weeks, less than $400, 25 words or less. Cambridge gives the same countable/uncountable split.
We had less complaints this month.
We had fewer complaints this month, and less noise.
The full table: 45 commonly confused words#
Scan for the pair you are unsure about. The last column is the quickest test we know for each.
| Pair | First word means | Second word means | Quick test |
|---|---|---|---|
| affect / effect | to influence (verb) | a result (noun); to bring about (verb) | "the ___" = effect |
| their / there / they're | belonging to them | that place; "there is" | they're = they are |
| its / it's | belonging to it | it is / it has | expand to "it is" |
| your / you're | belonging to you | you are | expand to "you are" |
| whose / who's | belonging to whom | who is / who has | expand to "who is" |
| then / than | at that time; next | in comparison with | comparing? than |
| lose / loose | to misplace; fail to win | not tight | loose has room (oo) |
| to / too / two | toward; infinitive marker | also; excessively | "too" has too many o's |
| compliment / complement | praise | something that completes | complement completes |
| principal / principle | chief; head person; loan sum | a rule or belief | principle = rule (both end in -le) |
| fewer / less | smaller number (countable) | smaller amount (mass) | can you count them? |
| accept / except | to receive, agree to | excluding | except excludes (ex-) |
| advice / advise | a recommendation (noun) | to recommend (verb) | advice rhymes with ice, a thing |
| imply / infer | to suggest without saying | to conclude from evidence | speakers imply, listeners infer |
| lay / lie | to put something down (takes an object) | to recline | lay what? needs an object |
| farther / further | more distance (physical) | more extent or degree | farther has "far" |
| weather / whether | atmospheric conditions | if (introduces alternatives) | whether = "if or not" |
| stationary / stationery | not moving | writing paper | e for envelope |
| discreet / discrete | tactful, careful | separate, distinct | discrete's e's are separated by t |
| ensure / insure | to make certain | to cover with insurance | insurance = insure |
| elicit / illicit | to draw out (a response) | illegal | illicit ~ illegal |
| allude / elude | to refer to indirectly | to escape | elude = escape |
| capital / capitol | seat of government; money; uppercase | the building where a legislature meets | capitol has a dome (o) |
| cite / site / sight | to quote as evidence | a location; a website | sight = seeing |
| desert / dessert | arid land; to abandon | sweet course | dessert: you want seconds (ss) |
| emigrate / immigrate | to leave a country | to enter a country | e = exit, i = in |
| eminent / imminent | distinguished | about to happen | imminent = immediate |
| lead / led | to guide (present); a metal | past tense of lead | past tense is led |
| passed / past | went by (verb) | earlier time; beyond | verb? passed |
| peak / peek / pique | summit | a quick look | pique = provoke (interest) |
| rein / reign | strap that controls a horse | a monarch's rule | free rein, horse imagery |
| breath / breathe | air taken in (noun) | to inhale and exhale (verb) | the e makes it a verb |
| bare / bear | uncovered | to carry; the animal | bear with me |
| brake / break | device that stops a vehicle | to shatter; a pause | brake pedal |
| council / counsel | an assembly | advice; a lawyer; to advise | counsel = counselor's job |
| lightning / lightening | flash in a storm | making lighter | no e in the storm |
| precede / proceed | to come before | to go forward | pre = before |
| role / roll | a part or function | to turn over; a bread roll; a list | actors play roles |
| altogether / all together | completely | everyone in one place | can you split them? all together |
| maybe / may be | perhaps (adverb) | might be (verb phrase) | swap in "might be" |
| everyday / every day | ordinary (adjective) | each day | swap in "each day" |
| loath / loathe | reluctant | to hate | the e makes it a verb |
| borrow / lend | to take temporarily | to give temporarily | direction of the item |
| comprise / compose | the whole comprises the parts | the parts compose the whole | avoid "comprised of" in formal copy |
| assure / ensure | to tell someone confidently | to make certain | you assure a person |
Sources for the less obvious rows: Cambridge's guides to imply or infer, advice or advise, farther or further, altogether or all together and maybe or may be. The American Heritage note on infer puts it neatly: a speaker implies; a reader or listener infers.
A note on "comprised of"#
The traditional rule is that the whole comprises the parts (The Union comprises 50 states). Is comprised of is very common, and objection to it has softened: the American Heritage Usage Panel found 53 percent objecting in the 1960s, 35 percent in 1996 and 32 percent in 2011. It is not wrong in casual writing, but in formal or legal copy, consists of or is made up of avoids the argument entirely.
Why these errors happen (and how to catch them)#
Almost every pair above is a homophone or near-homophone. When you type quickly, your fingers follow sound, not meaning, which is why fluent writers make these mistakes in emails they would never make in a careful essay. Three habits help:
- Expand contractions in your head. Read every it's, you're, they're and who's as the full two words. If the sentence breaks, you wanted the possessive.
- Search for your personal list. Most people have three to six pairs they reliably get wrong. Before sending anything important, use find-in-page on those exact words.
- Read it aloud, slowly. This catches meaning errors that silent skimming skips. It will not catch homophones, but it will catch the sentence around them.
If the problem is less "which word" and more "my fingers hit the wrong keys," that is a typing-accuracy issue rather than a vocabulary one. A few minutes a day of free typing accuracy drills does more for stray letters than any amount of rereading. For spelling rather than word choice, see our list of commonly misspelled words; for structure, see common grammar mistakes.
Frequently asked questions
Why doesn't spell-check catch confused words?
Because each word is spelled correctly. Their, there and they're are all real words, so a basic spell-checker has nothing to flag. Grammar checkers do better, but they still guess from context and miss plenty.
Is 'effect' ever a verb?
Yes. As a verb, effect means to bring something about, as in to effect a cure or to effect change. The American Heritage Dictionary notes that effect savings (create new savings) and affect savings (change existing savings) mean different things.
Is 'affect' ever a noun?
Rarely, and mainly in psychology, where it means an observable emotion (a person with a flat affect). It is stressed on the first syllable. In everyday writing the noun you want is almost always effect.
Is it 'fewer than' or 'less than' for money and time?
Use less than for amounts of time, money and distance even though they are plural: less than $400, less than three weeks. The American Heritage usage note treats these as well-established exceptions to the countable rule.
What is the fastest way to stop mixing these up?
Learn one test per pair (swap in they are for they're, swap in it is for it's), then proofread specifically for the five or six pairs you personally get wrong. Most people have a short personal list.
Sources
Every factual claim on this page links to one of these. Checked October 2026. See how we source.
- Cambridge Dictionary, English Grammar Today: Affect or effect? dictionary.cambridge.org
- American Heritage Dictionary: usage note at 'affect' ahdictionary.com
- Cambridge Dictionary: There, their or they're? dictionary.cambridge.org
- Cambridge Dictionary: It's or its? dictionary.cambridge.org
- American Heritage Dictionary: usage note at 'then' ahdictionary.com
- American Heritage Dictionary: usage note at 'complement' ahdictionary.com
- American Heritage Dictionary: usage note at 'principal' ahdictionary.com
- Cambridge Dictionary: Principal or principle? dictionary.cambridge.org
- American Heritage Dictionary: usage note at 'less' ahdictionary.com
- Cambridge Dictionary: Less or fewer? dictionary.cambridge.org
- American Heritage Dictionary: usage note at 'infer' ahdictionary.com
- Cambridge Dictionary: Imply or infer? dictionary.cambridge.org
- Cambridge Dictionary: Advice or advise? dictionary.cambridge.org
- Cambridge Dictionary: Farther, farthest or further, furthest? dictionary.cambridge.org
- Cambridge Dictionary: Altogether or all together? dictionary.cambridge.org
- Cambridge Dictionary: Maybe or may be? dictionary.cambridge.org
- American Heritage Dictionary: usage note at 'comprise' ahdictionary.com