✍️ English & Grammar · Chapter 4

Sentence correction: the 8 error types

Placement tests don't invent errors. They recycle eight of them — so stop reading each sentence hoping something sounds wrong, and start checking a list.

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The basics

Sentence correction is the test format — and the editing skill — of finding the one error in a sentence and fixing it with the smallest change.

The problem it solves: reading a sentence and asking "does this sound wrong?" fails exactly when it matters — long sentences, a clock running, English not your first language. Placement tests at TCS, Infosys or any MBA entrance don't invent new errors; they recycle the same eight.

The mental model: a pilot's pre-flight checklist. You don't listen for problems, you check a fixed list in a fixed order:

1. Subject-verb agreement
2. Tense
3. Pronoun reference
4. Parallelism
5. Modifier placement
6. Comparison
7. Articles and prepositions
8. Redundancy

Agreement and tense are about half of all questions, so they go first.

When your ear and the checklist disagree, the checklist wins.

Explained

Most people attempt sentence correction by feel: read it, see if something sounds off, guess.

That works until the sentence is long, or until English isn't the language you think in — which is exactly when the test gets hard.

The alternative is to scan for eight specific things, in a fixed order. It's slower for the first ten questions and much faster for the next thousand, because you stop re-deriving what to look for.

The pre-flight checklist

Pilots have flown the same aircraft a thousand times. They still read the checklist aloud before every take-off.

Not because they've forgotten — because memory is unreliable under time pressure, and a list isn't. The checklist doesn't make them better pilots; it makes them consistent ones.

A sentence-correction section is thirty questions in twenty minutes with a clock visible. That is precisely the condition under which "does this sound right?" fails and a list holds.

The scan, in order

Ordered by frequency. Agreement and tense together account for roughly half of what tests throw at you, so they go first.

The four you probably haven't studied

Types 1, 2, 7 have their own lessons. These four are the ones people meet for the first time in an exam.

Parallelism — items in a list must share a grammatical shape.

✗ The job extracts data, transformation, and it loads to S3.
✓ The job extracts, transforms, and loads data to S3.
✗ She is responsible for ingestion, modelling and to monitor the DAGs.
✓ …for ingestion, modelling and monitoring.

Modifier placement — a describing phrase attaches to whatever sits next to it.

✗ Running slowly, the engineer restarted the pipeline.
   (the engineer was running slowly)
✓ The engineer restarted the pipeline, which was running slowly.

✗ After reviewing the logs, the root cause became clear.
   (the root cause reviewed the logs — a 'dangling' modifier)
✓ After reviewing the logs, we identified the root cause.

Comparison — you must compare like with like.

✗ Spark's performance is better than Pandas.
   (performance compared to a library)
✓ Spark's performance is better than Pandas's.
✗ Our latency is lower than last year.
✓ Our latency is lower than it was last year.

Pronoun reference — every pronoun needs exactly one possible antecedent.

✗ The consumer polled the broker, but it had crashed.
   (which one crashed?)
✓ The consumer polled the broker, but the broker had crashed.
✗ We deployed and rolled back the config, which caused the outage.
   (what caused it — the deploy, the rollback, or the config?)

Run the checklist on one sentence

Four errors, found by running a list rather than by listening. Notice the checklist also stopped you flagging the tense, which was fine — knowing what isn't an error is half the speed.

Name the error type

Each sentence has exactly one error. Say which of the eight types it is.

1. The data pipeline, along with its tests, were deployed yesterday.
2. Having reviewed the logs, the bug was obvious.
3. Our query is faster than the old system.
4. The job extracts data, cleaning it, and then it loads to Snowflake.
5. He returned back the laptop to the IT team.
6. Each of the engineers have their own environment.

Reverse-engineer the correction

A colleague edits your design doc. Original on the left, their edit on the right:

You: "Neither the producers nor the consumer were configured correctly, which caused the outage. After analysing the metrics, the partition key was found to be skewed, and the team is responsible to fix it, monitoring lag and to add alerts."

>

Them: "Neither the producers nor the consumer was configured correctly, and that misconfiguration caused the outage. After analysing the metrics, we found the partition key was skewed. The team is responsible for fixing it, monitoring lag and adding alerts."

Sitting the actual test

Sentence correction usually appears as 20–30 questions in a timed verbal section — roughly 40 seconds each. That budget shapes the strategy.

Work by elimination, not by rewriting. In a multiple-choice format, find the error first, then discard every option that doesn't fix it. Two options usually die immediately.

Scan the options vertically. Where the choices differ tells you what's being tested before you've finished reading them. If three options vary between has and have, the question is agreement and you can go straight to finding the subject.

Don't fix what isn't broken. Many options change something correct into something also correct but longer. The shortest option that fixes the actual error is usually right.

Watch for the trap of ear. "Neither of them are ready" sounds fine to most people and is wrong on a test. When your ear and the checklist disagree, the checklist wins — that's the entire reason you have one.

If you can't find the error in 40 seconds, mark and move. A question you leave costs you one mark; a question you spend three minutes on costs you four.

Words to know

In two minutes

• Tests recycle eight error types; scanning a list beats listening for what sounds wrong.
• Checklist order: agreement, tense, pronoun, parallelism, modifier, comparison, article/preposition, redundancy.
• Agreement: cross out the middle. Parentheticals (along with, as well as) never change the subject's number.
• Every pronoun needs exactly one antecedent; a 'which' pointing at a whole clause is a red flag.
• Lists share one shape; an opening -ing phrase must attach to whoever did the action.
• Compare like with like: Spark's performance vs Pandas's, not vs Pandas.
• In a timed test, read how the options differ first, eliminate, and pick the shortest option that fixes the error.
• At work, the same eight are the ways a postmortem or ticket becomes ambiguous — run the list on anything someone will act on.

Test yourself

There are 11 questions, 3 puzzles and 7 recall cards for this lesson in the app — the recall cards come back on later days, just before you would forget.