Compound Sentences

A compound sentence joins two or more independent clauses — clauses that could each stand alone as a complete sentence — and gives them equal grammatical weight. The effect is balance and coordination: no clause is subordinate to another, and the reader understands that the ideas carry parallel importance. This is the structure you reach for when you want to link related but self-sufficient thoughts without subordinating one to the other.

The most straightforward way to form a compound sentence is with a coordinating conjunction. The seven coordinating conjunctions in English are for, and, nor, but, or, yet, and so — remembered by the acronym FANBOYS. Each signals a specific logical relationship: and adds information, but and yet contrast, or presents alternatives, so indicates consequence, for introduces a reason, and nor joins negative alternatives. The punctuation rule is simple: place a comma before the conjunction. She wanted to play tennis, but he wanted to play basketball. I came, and I sat.

Correlative conjunctions — pairs like either…or, neither…nor, not only…but also — offer a more emphatic way to coordinate clauses. Either you leave, or I will. Not only did she finish the project, but she also delivered it early. The parallel structure they create heightens the contrast or connection between the two clauses.

When you want a tighter, more sophisticated join, use a conjunctive adverb: however, therefore, moreover, nevertheless, meanwhile, consequently. These do not grammatically join clauses in the way conjunctions do — they are adverbs that signal logical relationships. As a result, they require stronger punctuation: a semicolon before and a comma after. I was tired; however, I finished the work. The data was incomplete; therefore, we delayed the report.

A semicolon alone can join two independent clauses when they are closely related and the logical connection is obvious without a conjunction. I made the cake; my sister decorated it. This construction works best when the second clause directly parallels or completes the first.

Two common errors plague compound sentences. A comma splice happens when two independent clauses are joined with only a comma and no conjunction: I went, I saw is incorrect — use a semicolon (I went; I saw) or a conjunction (I went, and I saw). A run-on sentence merges clauses with no punctuation at all: I went I saw I conquered is unreadable. Both errors are fixed by the same tools: a semicolon, a coordinating conjunction with a comma, or breaking the sentence into two.