Run-On Sentences: The Rules Explained Simply
The essential rules of run-on sentences with examples you can apply immediately.
The core idea behind run-on sentence
Most grammar rules are simpler than they look. Run-on sentence comes down to two or more independent clauses joined with no punctuation or wrong punctuation, and once that idea clicks, the details fall into place.
A run-on sentence jams together two or more independent clauses with no punctuation or the wrong kind. A fused run-on has none; a comma splice is a type of run-on joined by a comma.
What follows is the short list of rules that cover almost every case you will meet in everyday writing.
Length alone does not make a run-on, the missing punctuation between clauses does, so check the joints of any long sentence.
After fixing several run-ons, vary your sentence lengths so the prose does not turn choppy.
A period is the simplest cure, but a semicolon or a subordinating word can keep related ideas together smoothly.
A coordinating conjunction with a comma, like and or but, keeps two related clauses together without fusing them.
The rules, in plain terms
- Two independent clauses cannot sit together without punctuation.
- A period turns each clause into its own sentence.
- A semicolon joins closely related clauses without a conjunction.
- A comma plus a conjunction like and or but also works.
- Subordinating one clause with because or since is another clean fix.
Each rule with a quick example
| Rule | Example | Note |
|---|---|---|
| Two independent clauses cannot sit together without punctuation. | Two independent clauses cannot sit together without punctuation. | Standard usage. |
| A period turns each clause into its own sentence. | A period turns each clause into its own sentence. | Standard usage. |
| A semicolon joins closely related clauses without a conjunction. | A semicolon joins closely related clauses without a conjunction. | Standard usage. |
| A comma plus a conjunction like and or but also works. | A comma plus a conjunction like and or but also works. | Standard usage. |
| Subordinating one clause with because or since is another clean fix. | Subordinating one clause with because or since is another clean fix. | Standard usage. |
Some points, like collective nouns and singular they, depend on your style guide. When a rule has a judgment call, follow the guide your field uses.
Run-on sentence rules at a glance
Why these rules exist
Grammar rules are not arbitrary hoops. Each one exists to remove ambiguity, so the reader gets the meaning you intended on the first read.
Run-on sentence in particular keeps the relationship between words clear, which is why breaking it tends to confuse readers more than it offends them.
When you know the reason behind a rule, it becomes much easier to remember and to apply under pressure.
A period is the simplest cure, but a semicolon or a subordinating word can keep related ideas together smoothly.
Length alone does not make a run-on, the missing punctuation between clauses does, so check the joints of any long sentence.
After fixing several run-ons, vary your sentence lengths so the prose does not turn choppy.
Applying the rules as you edit
- 1Read for the core relationship
Check the central words first, since that is where most of these rules apply.
- 2Test each rule against the sentence
Run through the short list above and flag anything that breaks.
- 3Fix and confirm
Apply the rule, then reread to be sure the sentence still means what you intended.
Rules serve clarity. Learn the few that govern run-on sentence, and the rest of your editing gets faster.
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