Definition · Plain-language
Compound sentences
A compound sentence joins two or more independent clauses using a coordinating conjunction (for, and, nor, but, or, yet, so — FANBOYS) or a semicolon.
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Structure and the FANBOYS rule
The seven coordinating conjunctions — for, and, nor, but, or, yet, so — are remembered by the acronym FANBOYS. Each introduces the second independent clause and signals the logical relationship between the two: and adds information, but shows contrast, so shows result, or presents an alternative, nor negates both clauses, yet introduces a concession, and for (formal) gives a reason. The standard structure is: independent clause + comma + coordinating conjunction + independent clause. Example: "The study was rigorous, but the sample size was limited." The comma before the conjunction is required when both sides are full independent clauses; it is omitted when the conjunction joins only two words or phrases, not two clauses: "She worked quickly and efficiently" needs no comma.
Using a semicolon instead of a conjunction
A semicolon can replace the coordinating conjunction and its comma entirely when the two independent clauses are closely related in meaning: "The deadline was firm; the team worked through the night." This construction is more formal and is common in academic prose. A semicolon can also be used with a conjunctive adverb (however, therefore, moreover, nevertheless, consequently) followed by a comma: "The results were positive; however, further trials are needed." This is not the same as a FANBOYS construction — conjunctive adverbs are adverbs, not conjunctions — but it achieves a similar joining effect. Do not use a comma alone to join two independent clauses; that produces a comma splice, one of the most common punctuation errors.
Compound sentences in academic and professional writing
Compound sentences are effective when two ideas carry equal weight and a close logical connection. They signal balance, contrast or consequence without subordinating one idea to the other. In academic writing, compound sentences often present paired findings or contrasting interpretations: "The intervention group showed improvement, but the control group remained stable." For variety, mix compound sentences with simple and complex ones to avoid a plodding, list-like rhythm. Overly long compound chains — joining three or four clauses with repeated and — weaken analytical writing; break them into shorter units or restructure with subordination. Check that both clauses are genuinely independent before using a comma + conjunction; a comma before and joining only two verbs or nouns is unnecessary.
Key facts
At a glance
- Definition: two or more independent clauses joined by a coordinating conjunction or semicolon
- FANBOYS: for, and, nor, but, or, yet, so — the seven coordinating conjunctions
- Comma rule: place a comma before the conjunction when joining two independent clauses
- Semicolon option: replaces comma + conjunction when clauses are closely related
- Contrast with complex: compound clauses are equal; complex sentences have a dependent clause
- Common error: comma splice — using only a comma to join two independent clauses without a conjunction
- Academic use: effective for showing balance, contrast or result between equal ideas
Common misconceptions
What people often get wrong
Often heard: Any sentence with "and" or "but" in it is a compound sentence.
Actually: The conjunction must join two full independent clauses. "She read and summarised the article" uses and to join two verbs, not two clauses — that is a simple sentence with a compound predicate.
Often heard: A semicolon can replace any comma in a sentence.
Actually: A semicolon joins two closely related independent clauses. It cannot replace commas used in lists, after introductory phrases, or around non-restrictive elements. Misusing semicolons as strong commas is a common error.
Often heard: Compound sentences and complex sentences are the same thing.
Actually: In a compound sentence both clauses are independent and equal. In a complex sentence one clause is dependent (subordinate) and cannot stand alone. The joining words are also different: FANBOYS vs subordinating conjunctions.
Common questions
FAQ
What is a compound sentence?+
A compound sentence joins two or more independent clauses using a coordinating conjunction (for, and, nor, but, or, yet, so) preceded by a comma, or using a semicolon. Each clause could stand alone as a grammatically complete sentence. The clauses are of equal rank, which distinguishes compound from complex sentences, where one clause is subordinate.
What are the FANBOYS conjunctions?+
FANBOYS is a mnemonic for the seven coordinating conjunctions: For, And, Nor, But, Or, Yet, So. Each signals a different relationship: and adds, but contrasts, so shows result, or offers an alternative, nor negates both parts, yet concedes, and for (formal) gives a reason. A comma is placed before the FANBOYS conjunction when it joins two independent clauses.
Is a semicolon the same as a comma before "and"?+
Both join two independent clauses, but differently. A semicolon stands alone: "The grant was approved; the team expanded." A comma-plus-conjunction is more explicit about the relationship: "The grant was approved, and the team expanded." A semicolon is more formal and implies the reader can infer the connection. Both are correct; choose based on tone and emphasis.
What is a compound sentence example?+
Here are five examples: "The data was collected in 2023, and the analysis took six months." "She submitted the draft, but the editor requested revisions." "The funding was approved; the project could now begin." "You can register online, or you can attend in person." "The results were promising, yet the methodology needed refinement."
Going deeper
