Sentence types: simple, compound and complex

A clause is a group of words with its own subject and verb. An independent clause makes complete sense alone and can stand as a sentence; a dependent (subordinate) clause starts with a word like because, although, when, or if, and leaves the reader waiting for more.

Every sentence type is simply a different combination of these two building blocks. Count the clauses and check their kind, and you can name any sentence — which is exactly the skill you need to control variety in IELTS writing.

• The ferry departs at noon.(independent clause — a complete simple sentence)
• Because the ferry departs at noon.(dependent clause alone — it cannot stand as a sentence)
• We packed early because the ferry departs at noon.(dependent clause attached to a main clause)

A simple sentence contains exactly one independent clause: one subject-verb pairing that stands alone. It can still carry a compound subject, a compound verb, or long descriptive phrases — none of those add a second clause.

Simple does not mean short or basic. A well-placed simple sentence after two longer ones gives your writing rhythm and lands a point with force, which is why skilled writers keep them in the mix deliberately.

• Dhaka's rickshaws outnumber its buses.(one clause — simple)
• My flatmate and I cook and eat together every Sunday.(compound subject and compound verb, still one clause)
• The delegates from twelve countries arrived at the conference centre before sunrise.(long, but still simple — one subject-verb pair)

A compound sentence joins two independent clauses with a comma plus a coordinating conjunction — the FANBOYS set: for, and, nor, but, or, yet, so. Both clauses carry equal weight, so compound sentences suit ideas of matching importance: two parallel facts, a contrast, or a cause with its result.

A semicolon can replace the comma-plus-conjunction when the two clauses are closely related. What a comma can never do is join two independent clauses by itself — that error is the comma splice, covered in its own lesson.

• The presentation ran long, but nobody seemed to mind.(comma + but joins two equal clauses)
• You can pay the deposit now, or you can wait until Friday.
• The signal dropped, we lost the recording.(a comma alone cannot join two clauses → The signal dropped, and we lost the recording.)

A complex sentence attaches at least one dependent clause to a main clause with a subordinator: because, although, if, when, while, until, since, and others. The subordinate clause is grammatically lower in rank — it explains, qualifies, or frames the main statement.

Order controls the comma. When the subordinate clause comes first, follow it with a comma; when it comes after the main clause, you usually need no comma at all. This one punctuation habit removes a whole family of errors from your writing.

• Although the museum was free, hardly anyone visited.(fronted clause + comma)
• Hardly anyone visits the archive unless a big exhibition opens.(no comma when the subordinate clause comes second)
• While the app was updating we lost our booking.(fronted clause needs a comma → While the app was updating, we lost our booking.)

A compound-complex sentence combines both patterns: at least two independent clauses plus at least one dependent clause. Used sparingly, it shows top-level control; used constantly, it buries your argument.

The IELTS Band 6 speaking descriptor rewards 'a mix of simple and complex structures', and Band 7 asks for a range used with flexibility. In practice that means deliberate variety: open a paragraph with a complex topic sentence, support it with a compound sentence, and close the point with a short simple one. Variety with accuracy is the target — never length for its own sake.

• When the flood warning came, the market closed early, and traders moved their stock upstairs.(compound-complex: one dependent + two independent clauses)
• Nobody argued.(a short simple sentence adds punch after longer ones)