08 — Sentence structure: run-ons, fragments & comma splices

What this fixes for you: your habit of writing one long sentence with no full stops, so your commits, PRs, and Slack messages read clearly the first time — no re-reading needed.

The rule in 30 seconds

• A complete sentence has three things: a subject (who/what), a verb (the action), and a complete thought (it can stand alone). Example: “The build failed.”
• Run-on = two complete sentences jammed together with no break: “the build failed i pushed a fix”. Wrong.
• Comma splice = two complete sentences joined by only a comma: “the build failed, i pushed a fix”. Still wrong — a comma is too weak to glue two sentences.
• You have four legal ways to join or separate them: a full stop ., a semicolon ;, a comma + conjunction (and / but / so), or a subordinating word (because / when / after / if).

Why this trips you up

You chain everything into one breathless line and drop every full stop — exactly like your real message: “can u do reaseach on grammer for me and teach me i already know but as of now i am making so much mistake.” That is three or four sentences with no breaks, no capitals, and a couple of spelling and count errors riding along. In code you break logic into small functions; do the same with sentences — one idea per sentence, then stop.

See it / fix it

❌ What you tend to write	✅ Correct	Why
the build failed i pushed a fix	The build failed. I pushed a fix.	Run-on. Two thoughts → two sentences. Capital I, full stops added.
the tests pass, the deploy is green	The tests pass. The deploy is green.	Comma splice — a comma can’t join two sentences. Use a full stop.
i refactored the service it is faster now	I refactored the service, and it is faster now.	Run-on. Comma + and joins two complete thoughts.
we hit a 429, we should add a retry	We hit a 429, so we should add a retry.	Comma splice. Add so to show the cause → effect.
cache was stale users saw old prices	Cache was stale, which made users see old prices.	Run-on. A subordinate clause (which…) attaches the second idea.
merged the PR (as a standalone Slack line)	I merged the PR.	Fragment — missing the subject. Add I.
because the token expired (alone)	The request failed because the token expired.	Fragment — a because clause can’t stand alone; attach it to a full sentence.
i already know but as of now i am making so much mistake	I already know it, but right now I'm making so many mistakes.	Run-on + count error: mistake is countable → so many mistakes. Comma + but.
can u do reaseach on grammer	Can you do research on grammar?	Texting + spelling: u→you, reaseach→research, grammer→grammar; it’s a question → ?.
open pull request when ready it will trigger CI	Open a pull request when ready; it will trigger CI.	Missing article a; run-on fixed with a semicolon (two related thoughts).

Patterns to remember

The four fixes — pick one when you have two complete sentences:

Fix	Looks like	Use when
Full stop	It failed. I fixed it.	The two ideas are independent. Safest default — use this most.
Semicolon	It failed; I fixed it.	The ideas are closely linked and you want them in one line.
Comma + conjunction	It failed, so I fixed it.	You want to show the relationship: and (add), but (contrast), so (result).
Subordinate clause	Because it failed, I fixed it.	One idea depends on the other: because / when / after / if / which.

Mnemonics:

• “Two verbs, two subjects → needs a join or a stop.” If you can split the line into two standalone sentences, you must use one of the four fixes between them.
• “A comma is not glue.” A comma alone never joins two sentences. It always needs a conjunction (, and / , but / , so).
• Fragment test: read the chunk out loud alone. If it leaves you waiting for more (“Because the token expired…”), it’s a fragment — attach it.

In your daily writing

• Commit messages: one line, one idea. Fix stale cache so users see current prices beats fixed cache it was stale users saw old prices.
• PR descriptions: write short sentences, each ending in a full stop. Reviewers scan; a wall of run-on text gets skimmed and bugs get missed.
• Slack standups: Yesterday I finished the retry logic. Today I'm on the 429 handler. No blockers. — three clean sentences, not one chain.
• Code comments: // Token can expire mid-request, so we refresh before retrying. — comma + so shows cause. Avoid // token expired refresh and retry it works now.
• Bug reports: separate what happened from what you expected. The export returns an empty file. I expected the full order list. Two sentences, instantly clear.

Drills

Fix or choose. Don’t peek at the answer key until you’ve tried each.

1. Fix: the migration ran it dropped the wrong column we need a rollback
2. Fix: i opened the PR, the CI is still running
3. Choose A or B: (A) The cache was cold, so the first request was slow. (B) The cache was cold, the first request was slow.
4. Fill the blank with the best join: The API returned 500 ___ the database connection timed out. (. / ; / because)
5. Fix the texting + run-on: can u review my pr i think its ready but tests are flaky
6. Is this a complete sentence, a fragment, or a run-on? Restarting the worker queue.
7. Fix: we shipped the feature flag off by default users wont see it yet
8. Choose A or B: (A) I rebased onto main but there were conflicts. (B) I rebased onto main, but there were conflicts.
9. Fix the count + run-on: i made so much mistake in this commit i will clean it up
10. Fill the blank: ___ the token expired, the request failed. (Because / But / So)
11. Fix: deploy is green metrics look normal closing the incident
12. Fix the article + comma splice: open pull request, it triggers the build

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Answer key

1. The migration ran. It dropped the wrong column, so we need a rollback. — Split the first run-on with a full stop; join the cause/result with , so.
2. I opened the PR. The CI is still running. — Comma splice fixed with a full stop. Also capitalize I.
3. A. , so correctly joins two complete sentences. B is a comma splice (comma alone can’t join them).
4. because (or a full stop): The API returned 500 because the database connection timed out. — The second clause explains the first, so because reads best; . also works.
5. Can you review my PR? I think it's ready, but the tests are flaky. — u→you, its→it's (it is), question mark, and , but joins the contrast.
6. Fragment — no subject or finished thought. Fix: I'm restarting the worker queue.
7. We shipped the feature. The flag is off by default, so users won't see it yet. — Break the run-on; , so shows the result. Note won't with the apostrophe.
8. B. When but joins two complete sentences (“I rebased onto main” + “there were conflicts”), put a comma before it. A is missing the comma.
9. I made so many mistakes in this commit. I'll clean it up. — mistake is countable → so many mistakes with the plural -s; split the run-on with a full stop.
10. Because — Because the token expired, the request failed. The clause sets up the cause; note the comma after the opening subordinate clause.
11. Deploy is green. Metrics look normal. I'm closing the incident. — Three separate thoughts → three sentences (the last needs a subject, I'm).
12. Open a pull request; it triggers the build. — Add the article a; replace the comma splice with a semicolon (closely linked ideas) or a full stop.

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