09 — Commonly confused words

What this fixes for you: the small word mix-ups that make a clean PR or commit look careless — its/it’s, your/you’re, login vs log in, and friends. Get these right and your writing instantly reads as more senior.

The rule in 30 seconds

• If you can expand it to two words (it is, you are, they are), use the apostrophe version (it’s, you’re, they’re). If not, use the plain one (its, your, their).
• then = time/sequence; than = comparison.
• affect = the verb (to change something); effect = the noun (the result).
• Many of these are one word as a noun (login, setup, backup) but two words as a verb (log in, set up, back up).

Why this trips you up

You write fast, all day, in commits and Slack — and texting habits leak in (“u”, “ur”, no capitals), so the apostrophe and the missing letter slip past. You also tend to drop the small grammar signals (the plural -s, the article a/the), and these confusable pairs hide in exactly that same blind spot. None of this means you don’t know the rule — it means you’re moving fast and need a quick self-check.

See it / fix it

❌ What you tend to write	✅ Correct	Why
fix: button looses focus on close	fix: button loses focus on close	lose = a verb (to misplace). loose = not tight. One o.
your right, the migration was missing	you're right, the migration was missing	you’re = you are.
the API returns it's status code	the API returns its status code	its = belonging to it. No apostrophe (like his, hers).
this build is slower then the last one	this build is slower than the last one	Comparison → than.
how does this affect the cache? (meaning the result)	what's the effect on the cache?	Result/outcome → effect (noun).
please login to the dashboard and retry	please log in to the dashboard and retry	Here it’s a verb → two words: log in.
i updated the setup steps, see PR	I updated the setup steps. See the PR.	Noun setup is fine; but capitalize I, end the sentence, add the.
there going to revert there changes	they're going to revert their changes	they’re = they are; their = belonging to them.
accept for the timeout, all tests pass	except for the timeout, all tests pass	except = leaving out. accept = to agree/receive.
we had less errors after the fix	we had fewer errors after the fix	Countable (errors) → fewer. Uncountable (downtime) → less.
who's branch is this?	whose branch is this?	Ownership → whose. who’s = who is.
use JSON, e.g. the response body (meaning “that is”)	use JSON, i.e. the response body	i.e. = that is (clarify). e.g. = for example.

Patterns to remember

The apostrophe = “two words” test

Word	Expands to?	Use when
it’s	it is / it has	”it’s failing” = it is failing
its	(no expansion)	“its config” = the config belonging to it
you’re	you are	”you’re blocked”
your	(no expansion)	“your branch”
they’re	they are	”they’re merging”
their	(no expansion)	“their service”
there	(no expansion)	“deploy it there” / “there is a bug”
who’s	who is / who has	”who’s on call?“
whose	(no expansion)	“whose PR broke main?”

One word (noun) vs two words (verb) — the verb has a space:

Noun (one word)	Verb (two words)
a login screen	please log in
the setup is done	set up the env
run a backup	back up the DB

Trick: if you can put a word between the two halves (“set the env up”, “log quickly in”), it’s a verb → two words.

then vs than — a for compare (than / compare), e for sequence (then / first then next).

affect vs effect — Affect = Action (verb). Effect = End result (noun).

fewer vs less — if you can count them with an -s plural (3 errors, 5 retries) → fewer. If you can’t (less traffic, less memory) → less.

to / too / two — too = also or excessive (“too slow”). two = the number 2. to = everything else.

into vs in to — into = movement/result (“merge it into main”). in to = the words just land next to each other (“log in to the box” = log in + to the box).

accept vs except — accept = take it; except = exclude it.

In your daily writing

• Commit messages: the big four to scan for are its/it’s, lose/loose, then/than, login/log in. Example: fix: prevent session from being lost on log in (verb → two words).
• PR titles: comparisons sneak in — “smaller bundle than before”, not “then”.
• Slack standups: kill the texting leak. Write “your PR is ready”, not “ur PR is ready”; “they’re reviewing”, not “there reviewing”. Capitalize I and the first word.
• Code comments & docs: use e.g. for examples and i.e. to restate one specific thing — and put a comma after both: // retry on transient errors, e.g., 502 and 503.
• Quick self-check before you hit send: any apostrophe word? Expand it in your head. Any “login/setup”? Ask “is it a thing or an action?”

Drills

Fix or choose. Don’t peek at the key.

1. Fix: your going to want to rebase before you push
2. Choose: The new query is faster (then / than) the old one.
3. Fix: the cache keeps it's value after restart
4. Choose: Please (login / log in) and run the seeder.
5. Fix: we have less open tickets then last sprint
6. Choose: This change won’t (affect / effect) the public API.
7. Fix: accept for one flaky test, the suite is green
8. Fill the blank: ____ branch is this, and ____ reviewing it? (whose / who’s)
9. Fix (rewrite the learner’s own line): can u do reaseach on grammer for me and teach me i already know but as of now i am making so much mistake
10. Choose: Merge the hotfix (into / in to) main.
11. Fix: there service is down so there going to fail over
12. Choose: Use a real client, (e.g. / i.e.) curl or Postman.
13. Fix: the build looses the env vars during setup (one error is a word-choice, find it)
14. Choose: The retry count is (to / too / two) high.

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Answer key

1. You’re going to want to rebase before you push. — “you’re” = you are; capitalize the first word; end with a full stop.
2. than — it’s a comparison.
3. The cache keeps its value after restart. — “its” = belonging to the cache, no apostrophe.
4. log in — it’s a verb here, so two words.
5. We have fewer open tickets than last sprint. — tickets are countable → “fewer”; comparison → “than”.
6. affect — it’s the verb (to change something).
7. Except for one flaky test, the suite is green. — “except” = leaving out; capitalize the first word.
8. Whose branch is this, and who’s reviewing it? — “whose” = ownership; “who’s” = who is.
9. Can you do research on grammar for me and teach me? I already know it, but right now I’m making so many mistakes. — fixes: “you” not “u”, spelling “research”/“grammar”, capital “I”, a question mark, “many mistakes” (countable plural), and clearer wording.
10. into — one word for movement/result (merging X into Y).
11. Their service is down, so they’re going to fail over. — “their” = belonging to them; “they’re” = they are; comma before “so”.
12. e.g. — you’re giving examples, not restating one exact thing.
13. The build loses the env vars during setup. — “loses” (verb, one o); “setup” as a noun here is correct.
14. too — meaning excessive.

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Part of the Developer English course — see 00-index.md.