Splice two ropes, and you join them into one. Splice two main clauses by putting only a comma between them, however, and you get a faulty construction called a comma splice. Here are two perfectly good main clauses, each separate, each able to stand on its own as a sentence:

The detective wriggled on his belly toward the campfire. The drunken smugglers didn’t notice him.

Splicing those sentences with a comma makes for difficult reading.

Even more confusing than a comma splice is a fused sentence: two main clauses joined without any punctuation.

Lacking clues from the writer, a reader cannot tell where to pause. To understand the sentence, he or she must halt and reread.

The next two pages show five easy ways to eliminate both comma splices and fused sentences, also called run-ons. Your choice depends on the length and complexity of your main clauses and the effect you desire.

Neither sentence yields its meaning without a struggle. To point readers in the right direction, separate the clauses.

If both clauses are of roughly equal weight, you can use a comma to link them — as long as you add a coordinating conjunction after the comma.

A semicolon can connect two closely related thoughts, emphasizing each one.

If the second thought illustrates or explains the first, add it with a colon.

The only punctuation powerful enough to link two main clauses single-handedly is a semicolon, a colon, or a period. A lone comma won’t do the job except in the case of joining certain very short, similar main clauses.

Jill runs by day, Tom walks by night.

I came, I saw, I conquered.

Commas are not required with short, similar clauses; you can stick with semicolons to join all main clauses, short or long.

Jill runs by day; Tom walks by night.

I came; I saw; I conquered.

If one main clause is more important than the other or you want to give it more importance, make the less important one subordinate, which throws weight on the main clause. In effect, you show your reader how one idea relates to another: you decide which matters more.

If you want to cram more than one clause into a sentence, you may join two clauses with a conjunctive adverb. Conjunctive adverbs show relationships such as addition (also, besides), comparison (likewise, similarly), contrast (instead, however), emphasis (namely, certainly), cause and effect (thus, therefore), or time (finally, subsequently). These transitional words and phrases can be a useful way of linking clauses — but only with the right punctuation.

A writer might consider a comma plus the conjunctive adverb however enough to combine the two main clauses, but that glue won’t hold. Stronger binding — the semicolon along with a comma — is required.