Sentence structure: where grammatical range is built.
Four sentence types, two kinds of clause, and the connectors that join them. Control of complex sentences is the clearest single signal that a writer or speaker has moved past Band 6, and it is the most teachable grammar there is.
Why this matters. The grammar band descriptor turns on one phrase: a range of complex structures. A whole answer of short, simple sentences is capped, however clean each one is, because nothing in the grammar shows how the ideas relate. The lift comes from joining ideas on purpose, by coordination, by subordination, by relative clauses, so that the relationship is carried by the structure itself. The patterns are finite; once they are automatic, they raise every sentence you write.
Every sentence is built from clauses.
A clause is a subject and a verb. An independent clause stands on its own as a sentence; a dependent (subordinate) clause cannot, it leans on an independent one. The four sentence types are just different ways of combining them.
Simple
one independent clause
A single subject-verb idea that stands on its own. Correct and clear, but an answer built only from these reads as a Band 5 to 6 list.
The library closes at nine.
Compound
clause + coordinator + clause
Two equal ideas joined by a coordinator, the FANBOYS: for, and, nor, but, or, yet, so. Useful, but the lowest-value join, the ideas stay side by side as equals.
The library closes at nine, so I study at home after that.
Complex
independent + dependent clause
One idea made to depend on another with a subordinator (because, although, while, if, when…). This is the Band 7 structure: the grammar itself carries the logic.
Although the library closes at nine, I prefer to study there because it is quieter.
Compound-complex
two independent + one dependent
The full range, used sparingly. Powerful when it is controlled; a band-capping tangle when it is not. Reach for it once, not in every sentence.
The library closes at nine, so I study at home, although I work better when the building is quiet.
The two errors that cap accuracy
Two independent clauses cannot be joined by a comma alone (a comma splice) or by nothing at all (a run-on). “The library closes at nine, I study at home” and “The library closes at nine I study at home” are both wrong. Fix them four ways: a full stop, a semicolon, a coordinator (…, so I study…), or, best of all, by making one clause dependent (Because the library closes at nine, I study at home), which fixes the error and adds range.
What sentence range reads like at each band.
At Band 5
Mostly short, simple sentences, with attempts at longer ones breaking down into run-ons or comma splices. Clauses are joined with and, but and so, repeatedly; subordination is rare. Ideas often read as a list rather than a connected argument.
At Band 6
Mostly simple and compound sentences, joined with and, but and so. Complex sentences are attempted, but errors arrive with them: a missing comma after an opening clause, a subordinator that does not fit the meaning, a comma splice. The range is there in patches; the control is not.
At Band 7
A clear mix of simple and complex sentences, with subordinate and relative clauses used on purpose. Errors still occur, but they sit in the more ambitious sentences and do not block meaning. The complex sentences are doing a job, carrying contrast, cause or condition, rather than decorating.
At Band 8+
A wide range of structures, used flexibly and accurately. Most sentences are error-free; subordination, relative clauses and well-placed coordination shape the argument so the reader follows it without effort. Sentence length varies on purpose, a short sentence lands a point, a longer one develops it.
Pick the connector from the relationship, not at random.
Most weak complex sentences come from the wrong join: a because where the meaning is contrast, an and where one idea actually depends on the other. Decide the relationship first, then the connector follows.
| To show… | Use… | For example |
|---|---|---|
| Addition (equal weight) | and · also | The scheme cut costs, and it widened access. |
| Contrast | although · whereas · while | Although the scheme cut costs, access fell. |
| Cause | because · since · as | Access fell because the scheme cut staff. |
| Result | so · so that | Staff were cut, so access fell. |
| Condition | if · unless · provided that | Access will fall unless funding is restored. |
| Time | when · before · after · as soon as | After the scheme launched, complaints rose. |
| Detail about a noun | who · which · that (relative) | The scheme, which launched in 2019, cut costs. |
| Purpose | to · in order to · so that | The scheme was cut to save money. |
Two warnings. However, therefore and moreover are not conjunctions: they cannot join two clauses with a comma (that is the comma splice again), so start a new sentence or use a semicolon. And conditions (if / unless) open a structure of their own, with its own tense rules. Work through conditionals →
Ten to drill.
Identify the type, fix the join, or choose the version that shows the most range. Press Check answers for your score and the reason behind each one. Nothing is sent anywhere.
You can name the four types in a minute. Building them without thinking is the work.
Comma splices and dropped subordinators hide in long sentences, exactly where you cannot catch them yourself.
In a lesson I mark your writing against the grammar criteria and show you, line by line, where a simple sentence could carry more, or where a join has slipped. Lessons are £20 for fifty minutes, one to one, in proper British English; the first step is a free 25-minute introduction. This page is adapted from the grammar chapter of the forthcoming Ultimate Guide to IELTS Speaking.