Explanations rather than definitions. A dictionary tells you what each word means, which was never the problem — the problem is knowing which one you want while you are mid-sentence.
English has around a hundred and seventy thousand words in current use and almost nobody confuses any of them. The same twenty or thirty pairs cause nearly all of it, and they cause it for three reasons.
Some are identical in speech. Nothing distinguishes its from it's when you say them, so the distinction never gets practised in the years before you start writing seriously — it has to be learned deliberately, once, in a way that sticks.
Some have a gap so narrow that using the wrong one still communicates. Fewer for less does not stop anyone understanding you. It is noticed by exactly the readers whose opinion you were writing for.
And some have drifted. Disinterested once meant impartial and is now widely used to mean bored — which is fine in conversation and a problem in a document where impartiality is the point.
Rules do not stick. Affect is the verb, effect is the noun is correct, has been recited at you for twenty years, and you still pause — because recalling a rule under time pressure is a different task from knowing a word.
What works is a substitution you can hear. If influence fits, the word is affect. If result fits, it is effect. You are no longer retrieving a rule, you are checking whether a sentence sounds right, which you can already do.
Each page below leads with the substitution rather than the rule. If one of them works, you will not need to come back for that pair — which is the point of a reference page and not, we realise, the point of a page that wants visits.
Homophones. Nothing in speech distinguishes them, so the mistake only ever appears in writing — which is why it survives years of fluent talking.
Affect vs Effect
A clear, simple explanation of when to use "affect" versus "effect," with real examples for each.
Complement vs Compliment
A clear, simple explanation of when to use "complement" versus "compliment," with real examples for each.
discreet vs discrete
Discreet means tactful. Discrete means separate. The two "e"s in discrete are themselves separated.
Its vs It's
A clear, simple explanation of when to use "its" versus "it's," with real examples for each.
principal vs principle
Principal is a person or a sum of money, and means "main." Principle is a rule or belief. One is never the other.
stationary vs stationery
Stationary means not moving. Stationery means paper and pens. The difference is one letter, and there is a trick for it.
then vs than
Then is about time or sequence. Than is for comparisons. One vowel apart, and the distinction is absolute.
there vs their
There points to a place. Their shows possession. A one-letter difference, and a memory trick that makes it stick.
your vs you're
Your shows possession. You're is short for "you are." One quick substitution test tells you which one you need, every time.
The gap is narrow and real. Most readers will not notice the wrong one — but the ones who do are usually the ones marking, reviewing or signing it.
assure vs ensure
You assure a person. You ensure an outcome. And in American English, you insure property.
comprise vs compose
The whole comprises the parts. The parts compose the whole. "Comprised of" is the error to avoid.
continual vs continuous
Continual means repeatedly, with pauses. Continuous means without interruption. The difference matters in contracts.
farther vs further
Farther is for physical distance. Further is for everything else. British English mostly ignores the distinction.
fewer vs less
Fewer is for things you can count. Less is for quantities you cannot. The exceptions are more interesting than the rule.
historic vs historical
Historic means significant. Historical means relating to the past. Most old things are historical; few are historic.
imply vs infer
The speaker implies. The listener infers. Two ends of the same act of communication.
These have drifted. The word means something narrower, older or simply different from what common use suggests — and in formal writing the older sense is still the one being read.
Same root, different job in the sentence. Knowing which is which is a matter of what the word is doing rather than what it means.
Pairs that do not fit a pattern, and are simply worth getting right.
accept vs except
Accept means to receive or agree. Except means excluding. Opposite jobs, one letter apart.
advice vs advise
Advice is the thing you get. Advise is the act of giving it. The "s" is pronounced like a "z."
bring vs take
Bring moves something toward the speaker. Take moves it away. The right word depends on where you are standing.
cite vs site
Cite means to quote a source. Site means a location. A third, "sight," means vision.
elicit vs illicit
Elicit is a verb — to draw something out. Illicit is an adjective — illegal. Different parts of speech entirely.
emigrate vs immigrate
You emigrate from a country and immigrate to one. Same journey, described from opposite ends.
everyday vs every day
Everyday is an adjective meaning ordinary. Every day is two words meaning each day. The space changes the part of speech.
into vs in to
Into is a preposition of movement. In to is two words that happen to sit together. The difference is real.
lose vs loose
Lose is a verb — to misplace or be defeated. Loose is an adjective — not tight. The extra "o" changes everything.
passed vs past
Passed is the past tense of the verb "pass." Past is a noun, adjective or preposition. Never a verb.
If the problem is the sentence rather than the word, the word counter is free and unlimited, and cutting word count covers the structural edits that fix more than any single word choice will.