Run-on Sentences: Common Mistakes

Run-on sentences are one of the most common grammar mistakes in English writing. They happen when two or more independent clauses are joined without the correct punctuation or connecting words. Although they often sound natural in speech, they make written English confusing or unclear. In this guide, you’ll learn what causes run-on sentences, how to identify them, and how to fix them effectively.

What Is a Run-on Sentence?

A run-on sentence occurs when two or more complete thoughts (independent clauses) are joined incorrectly. In other words, each clause could stand alone as a full sentence, but they are combined without proper punctuation.

There are two main types of run-ons:

• Fused sentence: Two independent clauses joined with no punctuation.

  • ❌ I love Cebu it is a beautiful city.

• Comma splice: Two independent clauses joined only with a comma.

  • ❌ I love Cebu, it is a beautiful city.

Both are incorrect because the clauses are not properly separated or connected.

Why Run-on Sentences Are a Problem

Run-on sentences confuse readers and make your writing appear unpolished. Clear sentence boundaries are essential for professional, academic, and formal writing.

They reduce clarity

Readers may not understand where one idea ends and another begins.

They weaken emphasis

Important ideas can get lost in a long, unpunctuated stream of text.

They sound unprofessional

Frequent run-ons give the impression that your writing is rushed or unedited.

How to Identify Run-on Sentences

To spot a run-on, look for two or more independent clauses in one sentence that are not properly joined.

Tip: Try reading your sentence aloud. If you naturally pause or take a breath but there’s no punctuation, it’s likely a run-on.

Example:
❌ The bus was late we missed our class.
✅ The bus was late. We missed our class.

Common Causes of Run-on Sentences

1. Omitting punctuation between ideas

   • ❌ He opened his laptop it didn’t turn on.

   • ✅ He opened his laptop, but it didn’t turn on.

2. Overusing “and” or commas

   • ❌ She studied all night and she forgot to eat breakfast and she was late for class.

   • ✅ She studied all night, forgot to eat breakfast, and was late for class.

3. Writing as you speak
   In casual speech, we often join ideas naturally. Writing those same sentences without editing can lead to run-ons.

How to Fix Run-on Sentences

There are several effective ways to correct run-ons depending on your intended meaning.

1. Use a Period

The simplest fix is to separate the two clauses into complete sentences.

• ❌ She wanted to go shopping she didn’t have enough money.

• ✅ She wanted to go shopping. She didn’t have enough money.

2. Use a Semicolon

Use a semicolon (;) when the ideas are closely related.

• ✅ She wanted to go shopping; she didn’t have enough money.

3. Use a Comma and a Coordinating Conjunction

Join the clauses with a comma and one of the FANBOYS conjunctions (for, and, nor, but, or, yet, so).

• ✅ She wanted to go shopping, but she didn’t have enough money.

4. Use a Subordinating Conjunction

Make one clause dependent on the other to create a complex sentence.

• ✅ Although she wanted to go shopping, she didn’t have enough money.

5. Use a Conjunctive Adverb

Conjunctive adverbs like however, therefore, moreover, nevertheless can connect ideas with a semicolon.

• ✅ She wanted to go shopping; however, she didn’t have enough money.

Fused Sentences vs. Comma Splices

Both are incorrect in their original form, but can be fixed with proper punctuation or conjunctions.

Common Examples of Run-on Sentences and Fixes

How to Avoid Run-on Sentences

1. Keep sentences short and clear.
   Don’t try to include too many ideas in one sentence.

2. Check for multiple clauses.
   If both parts can stand alone, use punctuation or a conjunction.

3. Use conjunctions correctly.
   Remember the FANBOYS rule.

4. Read your work aloud.
   Listen for natural pauses — that’s often where punctuation belongs.

5. Revise carefully.
   Long, confusing sentences are often run-ons in disguise.

Run-on Sentences vs. Compound Sentences

A compound sentence is correctly joined with a comma and a coordinating conjunction. A run-on is not.

• ✅ Compound: I wanted to travel, but my passport expired.

• ❌ Run-on: I wanted to travel my passport expired.

Understanding this difference ensures grammatical precision.

Why Writers Create Run-on Sentences

Writers often create run-ons because they want to sound fluent or expressive. They believe that longer sentences show complexity or sophistication. However, clarity is more powerful than length. A mix of short and long sentences keeps writing natural and easy to follow.

Tips for ESL Learners

• Always make sure each sentence has one main subject and verb.

• Use a period or semicolon between two full ideas.

• Don’t rely on commas alone to connect sentences.

• Read native English examples to learn natural rhythm and punctuation.

Practice Exercise

Identify and correct the run-on sentences:

1. The rain stopped we went outside.

2. She loves to dance, it makes her happy.

3. They finished dinner they watched a movie.

Answers:

1. The rain stopped, so we went outside.

2. She loves to dance because it makes her happy.

3. After they finished dinner, they watched a movie.

Final Thoughts

Run-on sentences make your writing harder to understand and less professional. The key is to recognize when a sentence contains two complete ideas and connect them correctly using punctuation or conjunctions.

To summarize:

• Identify independent clauses.

• Separate or connect them properly.

• Read aloud to test for clarity.

Once you master this, your writing will flow smoothly — clear, concise, and free of run-on mistakes.

FAQs

What is a run-on sentence?

A run-on sentence occurs when two or more independent clauses (complete thoughts that could stand alone as sentences) are joined without proper punctuation or a suitable connecting word. The two most common forms are the fused sentence (no punctuation at all) and the comma splice (only a comma between independent clauses). Both forms obscure sentence boundaries and make your writing harder to read.

How do run-on sentences differ from compound sentences?

A compound sentence correctly joins two independent clauses with a comma and a coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so) or with a semicolon when ideas are closely related. A run-on sentence, by contrast, either omits the punctuation entirely or uses only a comma without a conjunction. For example:

• Correct compound: I wanted to travel, but my passport expired.
• Run-on (fused): I wanted to travel my passport expired.
• Run-on (comma splice): I wanted to travel, my passport expired.

What causes run-on sentences?

Common causes include writing exactly as you speak (spoken language often strings ideas together), overusing “and” to attach new thoughts, misunderstanding comma rules, and rushing through drafting without checking for independent clause boundaries. Writers who try to “sound advanced” may also cram too many ideas into one sentence, unintentionally creating run-ons.

How can I quickly test if a sentence is a run-on?

Try the period test. Split the sentence at the suspected boundary and place a period there. If both sides form complete sentences with a subject and a verb that express a full thought, you likely had two independent clauses. If no conjunction or proper punctuation connected them originally, you had a run-on or comma splice.

What are the main ways to fix a run-on sentence?

You have several options, each with a slightly different effect on tone and emphasis:

1. Use a period: Make two sentences. She was tired. She went home.
2. Use a semicolon: Connect closely related ideas. She was tired; she went home.
3. Add a comma and a coordinating conjunction: She was tired, so she went home.
4. Use a subordinating conjunction: Create a complex sentence. Because she was tired, she went home.
5. Use a conjunctive adverb with a semicolon: She was tired; therefore, she went home.

When should I use a semicolon instead of a period?

Use a semicolon when the two clauses are tightly linked in meaning and you want to highlight that connection without adding a conjunction. Semicolons are stylistically lean and useful for parallel or contrastive relationships. If the link is weak or you want a stronger pause, choose a period. If you want to spell out the relationship (contrast, cause, result), consider a conjunction or a conjunctive adverb.

What is a comma splice, and how is it different from a fused sentence?

A comma splice places a comma between independent clauses without a coordinating conjunction: The bus was late, we missed class. A fused sentence omits punctuation entirely: The bus was late we missed class. Both are run-ons; the comma splice at least attempts separation but does not meet grammatical standards. Fix both with one of the methods above.

Are long sentences always run-ons?

No. Length alone does not create a run-on. A long sentence can be perfectly correct if it uses proper punctuation and logical structure (e.g., semicolons, commas with coordinating conjunctions, and subordinating clauses). Conversely, even a short sentence can be a run-on if it joins two independent clauses incorrectly. Focus on grammatical relationships, not word count.

How do run-ons affect clarity and reader experience?

Run-ons blur idea boundaries, overload working memory, and bury key points. Readers slow down to re-parse logic, which weakens your message. In academic and professional contexts, persistent run-ons suggest careless editing or uncertain command of syntax. Clear separation and connection of ideas signal control, confidence, and respect for the reader’s time.

What are some reliable strategies to prevent run-ons during drafting?

Use these habits:

• One idea per sentence (first draft): Keep sentences short while drafting; combine later if needed.
• Read aloud: Where you pause naturally, check whether punctuation or a conjunction is needed.
• Highlight verbs: Multiple finite verbs with separate subjects may indicate multiple independent clauses.
• Scan for commas: If a comma separates two complete clauses without FANBOYS, you likely have a comma splice.
• Vary structure intentionally: Mix simple, compound, and complex sentences rather than chaining ideas with “and.”

Which conjunctions fix run-ons and which do not?

Coordinating conjunctions (FANBOYS) fix run-ons when paired with a comma: , for / , and / , nor / , but / , or / , yet / , so. Subordinating conjunctions (e.g., because, although, when, if, since, while) convert one clause into a dependent clause, also fixing run-ons. However, transitional words like however, therefore, moreover, nevertheless are not coordinating conjunctions. They must follow a semicolon or start a new sentence, not merely a comma.

Can a dash or colon fix a run-on?

Yes, in specific cases. A colon can join two clauses when the second explains or illustrates the first: I had one goal: finish on time. An em dash can join clauses for emphasis or interruption: He promised to help — he never showed up. Use these sparingly and ensure the relationship (explanation, amplification, sharp contrast) is clear. Do not use them to paper over unclear logic.

How can ESL learners avoid run-ons when their first language uses different punctuation rules?

Adopt a step-by-step approach: identify the subject and main verb of each clause; decide whether each clause is independent; choose a connector that reflects the logical relationship (cause, contrast, sequence, result); and apply the correct punctuation. Practice with sentence-combining exercises and read high-quality prose to absorb natural rhythm. Over time, you will internalize where English expects boundaries.

What are examples of common run-ons and correct revisions?

Examples and fixes:

• Run-on: We went to the beach it started to rain.
  Fix: We went to the beach, but it started to rain.
• Run-on: I studied all night I still failed the exam.
  Fix: I studied all night, yet I still failed the exam.
• Run-on: He didn’t call me I was worried.
  Fix: He didn’t call me, so I was worried.
• Run-on: The teacher arrived everyone became quiet.
  Fix: The teacher arrived, and everyone became quiet.
• Run-on: It’s late we should go home.
  Fix: It’s late; we should go home.

How do I choose the best fix when multiple options work?

Match the fix to your meaning and rhythm:

• Period for separation and emphasis on each idea.
• Semicolon to signal close connection without naming it.
• Comma + FANBOYS to make the relationship explicit (contrast, addition, result).
• Subordination to show one idea depends on or frames the other.
• Conjunctive adverb for formal transitions (; however, ; therefore, etc.).

What editing checklist can I use to catch run-ons?

Before finalizing, run through this checklist:

1. Underline every finite verb; ensure each independent clause is properly connected.
2. Search for commas between subjects + verbs on both sides; confirm you have , FANBOYS or change the punctuation.
3. Replace some long sentences with two short ones to improve pacing.
4. Read aloud and mark natural pauses; verify punctuation matches those pauses.
5. Confirm transitional adverbs are preceded by a semicolon or start new sentences.

Can style or creativity justify run-ons?

Occasional intentional run-ons appear in creative writing to mimic breathless speech or stream-of-consciousness. However, in academic, business, instructional, and journalistic contexts, they usually harm clarity and professionalism. Unless you have a deliberate rhetorical purpose and an audience receptive to experimentation, prefer standard punctuation and structure.

What practice exercise will help me master this?

Try this routine three times a week: write five sentences that intentionally combine two independent clauses. Then produce three corrected versions for each—one with a period, one with a semicolon, and one with a comma plus a coordinating conjunction. Next, revise two of them using subordination. This deliberate practice builds flexibility and helps you select the best fix for meaning, emphasis, and flow.

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