IELTS grammar: Building Complex Sentences

Grammatical Range and Accuracy rewards a genuine mix of sentence structures, and complex sentences are the single most reliable way to demonstrate that range without inflating your word count for its own sake. The specific error pattern examiners see under this heading isn't usually a lack of long sentences — most candidates under exam pressure naturally write some long sentences — it's a lack of genuine subordination. A sentence can be long, contain three clauses joined by "and," and still score as simple sentence structure repeated three times, because coordination (joining equal, independent ideas) is not the same grammatical achievement as subordination (making one idea depend on another). A complex sentence, in the strict grammatical sense used for IELTS marking, combines one independent clause — a clause that could stand alone as a complete sentence — with at least one dependent clause that cannot stand alone, connected by a subordinating conjunction such as "although," "because," "since," "while," "if," "unless," or a relative pronoun like "which" or "who." Understanding that distinction, and deliberately building sentences around it rather than around length, is what actually moves a script from Band 6 sentence variety toward Band 7 and above.

The most reliable way to build a genuine complex sentence is to start with two related simple sentences and ask which one is logically subordinate to the other — which one explains, conditions, contrasts with, or gives the reason for the other. "The city introduced a congestion charge. Traffic decreased by 15%." Read together, the first sentence is clearly the cause and the second the effect, so a subordinating conjunction expressing cause and result turns them into one genuinely complex sentence: "After the city introduced a congestion charge, traffic decreased by 15%," or "Traffic decreased by 15% after the city introduced a congestion charge." Notice the dependent clause can move to either end of the sentence — beginning or end — and IELTS specifically rewards varying that position across an essay, since opening every complex sentence with the dependent clause first becomes a noticeable, repetitive pattern by the third or fourth paragraph.

Different subordinating conjunctions express different logical relationships, and choosing the right one is itself part of Grammatical Range, since it shows the sentence structure is doing real argumentative work rather than being bolted on. "Because" and "since" both introduce a reason ("Since public transport remains limited, many residents continue to drive"). "Although" and "while" introduce a contrast or concession ("Although the policy reduced emissions, it increased costs for small businesses"). "If" and "unless" introduce a condition ("Unless funding increases, the programme will likely be cut"). Using "because" where the actual relationship is contrast, or "although" where the relationship is really cause and effect, produces a sentence that is grammatically complex but logically confused — a genuine error that costs marks under Coherence and Cohesion even though the grammar itself is technically fine.