Run-on sentences: find and fix them

Consider this short message: 'The gears are ready. The repair shop closes at five.' Each part expresses a finished thought that can stand alone as its own sentence. A run-on is not caused by having too many words or too many details; rather, it is a structural problem with how statements are joined. Before you choose any punctuation mark, test each statement independently. Identify who or what the statement concerns, locate the verb, and decide whether the thought is complete, since a subject and verb alone do not guarantee completeness.

When two complete thoughts meet in one sentence, writers often make one of two common errors. A fused sentence pushes two complete statements together with no punctuation between them. A comma splice places only a comma between two complete statements. A comma marks a slight pause, but it cannot hold two independent clauses together in standard writing. Both patterns confuse readers by hiding the sentence boundary.

You can practise this again in Run out of and Optative sentences: choosing hope or wish.

The most dependable way to repair a run-on sentence is to use a period. Place a period at the end of the first complete statement, and capitalize the first letter of the next word. This choice gives your reader time to absorb the first idea before moving to the next. In everyday workplace messages and quick text updates, two shorter sentences are usually clearer than a crowded compound sentence.

You can join two complete statements by placing a comma followed by a coordinating conjunction. Choose your connector by the meaning you want to convey. Use and to add related information, but to present an unexpected contrast, so to indicate a result, and or to offer an alternative. Sequence alone does not justify so; use so only when the second action happens as a direct outcome of the first.

A semicolon joins two complete statements that share an immediate, obvious connection. Both sides of the semicolon must be complete sentences that could stand alone. Do not add a coordinating conjunction like and or but directly after the semicolon. In everyday communication, separate sentences with periods are often simpler, but a semicolon remains a polished option when you want to highlight an intimate connection between two thoughts.

You can also repair a run-on sentence by making one clause depend on the other. Words like because and although turn a complete statement into a dependent clause. Because explains a cause, while although introduces a contrast. If you put the dependent clause first, put a comma after it. When the dependent clause follows the main clause, you usually do not need a comma. Never leave a dependent clause standing alone.

A frequent writing mistake is using however like the coordinating conjunction but. Placing a comma on both sides of however between two complete thoughts creates a comma splice. The transition word however is an adverb, not a conjunction. You must establish a complete sentence boundary before it using either a period or a semicolon. Follow however with a comma to signal a pause before the contrasting statement.

Do not assume that every long sentence is a run-on. A sentence can contain multiple clauses and many words if each clause is linked with correct punctuation and conjunctions. In addition, avoid inserting commas unnecessarily before and or but. When one subject carries out two actions joined by a conjunction, you do not place a comma before the conjunction because the second part lacks its own subject.

Selecting the best repair depends on your context and the relationship you want to emphasize between your complete thoughts. The reference table below compares five standard patterns for repairing run-on sentences. Review each structure to see how punctuation and connecting words define clause boundaries. Use this table as a quick guide when checking your work emails, class assignments, and daily text messages.

Read this short telephone dialogue about a bike repair: Mechanic: 'Your bicycle is ready, but our workshop closes at five o'clock today.' Marcus: 'My shift ends at six, so I cannot pick it up myself.' Mechanic: 'A colleague can collect it with your ticket, or you can come tomorrow.' When Marcus drafts a follow-up message asking a friend to collect the bike, he must preserve the reason, contrast, and choice from the conversation while avoiding run-on sentences.

Spoken English does not come with visible punctuation marks. When you listen to recorded English or a colleague speaking, speakers naturally pause between thoughts, but a pause alone cannot tell you whether a period, comma, or semicolon is appropriate. To understand the structure of spoken sentences, listen for connecting words like but, so, or because, and identify where one complete message ends and another begins.

To check your mastery, retrieve the stand-alone test from memory: determine who or what the statement concerns, locate the verb, and confirm that the thought is complete. When you encounter an unpunctuated message, locate where the first independent thought ends and the second begins. Once you identify that clause boundary, choose a repair method that preserves the author's meaning, such as a period or a coordinating conjunction, and explain why your punctuation fits that boundary.