Overview
Sentence Boundaries questions test whether students can identify complete sentences, recognize fragments and run-ons, and choose the correct punctuation or conjunction to fix boundary errors. These questions appear under the Boundaries sub-domain of Standard English Conventions. Every Boundaries question requires deciding whether two groups of words should be separated into distinct sentences, joined by a specific punctuation mark, or connected by a conjunction. Getting this right depends on identifying which clauses are independent and which are dependent.
Key Points
1. Independent vs. Dependent Clauses
An independent clause has a subject, a verb, and expresses a complete thought. It can stand alone as a sentence.
A dependent clause has a subject and a verb but does NOT express a complete thought. It begins with a subordinating conjunction (because, although, since, when, if, while, etc.) or a relative pronoun (who, which, that).
| Clause Type | Example | Can Stand Alone? |
|---|---|---|
| Independent | ”The experiment succeeded.” | Yes |
| Dependent | ”Because the experiment succeeded” | No |
| Independent | ”Researchers published the findings.” | Yes |
2. Sentence Fragments
A fragment is a group of words punctuated as a sentence that does not qualify as one. Fragments lack a subject, a main verb, or a complete thought.
| Fragment Type | Wrong | Correct |
|---|---|---|
| Missing subject | ”Ran across the field." | "She ran across the field.” |
| Missing verb | ”The scientist with the award." | "The scientist with the award spoke.” |
| Dependent clause only | ”Although the results were clear." | "Although the results were clear, the debate continued.” |
3. Run-On Sentences and Comma Splices
A run-on sentence (also called a fused sentence) joins two independent clauses with no punctuation at all.
A comma splice joins two independent clauses with only a comma — no conjunction.
Wrong: “The data was collected, it was analyzed immediately.” Wrong: “The data was collected it was analyzed immediately.”
Four ways to fix a run-on or comma splice:
| Fix | Example |
|---|---|
| Period (start new sentence) | “The data was collected. It was analyzed immediately.” |
| Semicolon | ”The data was collected; it was analyzed immediately.” |
| Comma + coordinating conjunction (FANBOYS) | “The data was collected, and it was analyzed immediately.” |
| Subordinating conjunction | ”After the data was collected, it was analyzed immediately.” |
4. Coordinating vs. Conjunctive Adverbs
Coordinating conjunctions (FANBOYS: For, And, Nor, But, Or, Yet, So) join two independent clauses when paired with a comma.
Conjunctive adverbs (however, therefore, moreover, consequently, furthermore, nevertheless) are NOT conjunctions. They cannot join two independent clauses with just a comma.
| Word | Type | Correct Usage |
|---|---|---|
| ”and” | Coordinating conjunction | ”She studied, and she improved." |
| "but” | Coordinating conjunction | ”He tried, but he failed." |
| "however” | Conjunctive adverb | ”She studied. However, she did not improve.” OR “She studied; however, she did not improve." |
| "therefore” | Conjunctive adverb | ”The results were unclear; therefore, the team repeated the test.” |
5. Colons and Dashes as Boundary Markers
A colon or em dash introduces explanatory or additional information. Both require a complete independent clause before them. Unlike a semicolon, what follows a colon or dash can be a full sentence OR a fragment.
Correct: “The experiment had one flaw: the sample size was too small.” Correct: “One factor mattered most — preparation.” Wrong: “The experiment’s flaw: was the sample size.” (colon follows incomplete clause)
Pitfalls and Common Mistakes
Pitfall 1: Comma Splice with Conjunctive Adverbs
Description: Students see words like “however,” “therefore,” or “consequently” and treat them like coordinating conjunctions, placing only a comma before them between two independent clauses.
Wrong: “The study was groundbreaking, however it had limitations.” Correct: “The study was groundbreaking; however, it had limitations.” OR “The study was groundbreaking. However, it had limitations.” Fix: Remember that conjunctive adverbs are not FANBOYS. They need either a semicolon before them or a period (starting a new sentence).
Pitfall 2: Mistaking a Long Phrase for a Sentence
Description: A long phrase or dependent clause at the start of a passage can look like a complete sentence, especially when it contains multiple verbs.
Wrong: “Having studied the migration patterns of monarch butterflies for over a decade.” (no main clause) Correct: “Having studied the migration patterns of monarch butterflies for over a decade, the researcher published her findings.” Fix: Ask: “Is there a main subject performing a main verb?” If not, the group of words is a fragment.
Pitfall 3: Joining Clauses with a Semicolon When One Side Is Dependent
Description: Students place a semicolon between an independent clause and a dependent clause, thinking any two clauses can be joined by a semicolon.
Wrong: “The team celebrated; because they had won.” Correct: “The team celebrated because they had won.” Fix: A semicolon requires a fully independent clause on BOTH sides. If one side starts with a subordinating conjunction, drop the semicolon.
Pitfall 4: Run-On Disguised by Length
Description: A very long sentence that strings two independent clauses together without proper punctuation. The length distracts from the missing boundary marker.
Wrong: “The researchers spent months analyzing the data from the 2023 expedition and they eventually discovered a pattern that had not been documented before.” Correct: “The researchers spent months analyzing the data from the 2023 expedition, and they eventually discovered a pattern that had not been documented before.” Fix: Identify the second independent subject and verb. If they form a new independent clause, a comma + coordinating conjunction is needed before the conjunction.
Related Entries
- Punctuation_Commas — Detailed rules on comma use including comma splices and introductory elements
- Punctuation_Semicolons_Colons_Dashes — When and how to use semicolons, colons, and dashes as boundary markers
- Parallel_Structure — Maintaining consistent grammatical form across clauses and lists
- Modifier_Placement — Placing introductory phrases correctly to avoid dangling modifiers
- Verb_Tense_Voice_Mood — Ensuring verbs within boundaries are in the correct form
Quick Reference Card
| Situation | Correct Fix | Wrong Fix |
|---|---|---|
| Two independent clauses | Period, semicolon, or comma+FANBOYS | Comma alone |
| Two independent clauses with “however” | Semicolon before “however” | Comma before “however” |
| Fragment (dependent clause only) | Add an independent clause | Leave as is |
| Colon/dash introduction | Must follow a complete clause | Cannot follow a fragment |
| Independent + dependent | No semicolon needed; use comma or nothing | Semicolon between them |