ACT English: Sentence Structure and Fragments

On the ACT English section, your ability to spot and fix broken sentences is non-negotiable. These questions test your fundamental grasp of grammar—not just rules, but how to apply them to make writing clear and effective. Mastering sentence boundaries means you can quickly transform confusing text into polished prose, directly boosting your score.

The Foundation: What Makes a Complete Sentence?

Before you can fix a broken sentence, you must reliably identify a correct one. An independent clause is a group of words that contains a subject and a predicate and expresses a complete thought. It can stand alone as a sentence. The subject is who or what the sentence is about, and the predicate (centered on a verb) tells what the subject is or does. For example, "The scientist conducted the experiment" is complete: "The scientist" (subject) "conducted the experiment" (predicate/verb). Every sentence correction you make on the ACT must result in one or more properly formed independent clauses.

Identifying and Correcting Sentence Fragments

A sentence fragment is an incomplete sentence masquerading as a complete one. It lacks either a subject, a complete verb, or the ability to express a full idea on its own. Fragments often trick you because they begin with a capital letter and end with a period, but they are structurally dependent on nearby sentences.

There are three common types of fragments you'll encounter:

1. Dependent Clause Fragments: These begin with a subordinating conjunction (e.g., because, although, while, since, if) or a relative pronoun (e.g., that, which, who). "Because the data was inconclusive." This has a subject and verb, but the word "because" makes it dependent; it leaves you waiting for the main point.
2. Phrase Fragments: These are often prepositional, verbal, or noun phrases missing a critical component. "Running quickly down the field." This has no subject. Who is running?
3. Missing-Verb or Missing-Subject Fragments: "A result of the complex calculations." This noun phrase has neither a true verb nor a clear subject performing an action.

To fix a fragment, you must attach it to a nearby independent clause or add the missing elements. Using our first example, you could attach it: "The team revised their hypothesis because the data was inconclusive." Alternatively, you could revise the fragment into its own sentence by removing the subordinating word: "The data was inconclusive."

Conquering Run-On Sentences and Comma Splices

While a fragment has too little, a run-on sentence (or fused sentence) has too much. It occurs when two or more independent clauses are joined without any punctuation or conjunction. "The lecture was fascinating it lasted for two hours." Here, "The lecture was fascinating" and "it lasted for two hours" are both independent clauses smashed together.

A comma splice is a specific, common type of run-on where two independent clauses are joined only by a comma. "The lecture was fascinating, it lasted for two hours." A comma alone is not strong enough to link two complete thoughts.

You have four primary strategies to correct run-ons and comma splices, and the best choice depends on the context and the author's intended relationship between the ideas.

1. Use a Period (or Semicolon): Create two separate sentences. This is a clear, strong fix when the ideas are distinct enough to stand alone. "The lecture was fascinating. It lasted for two hours." A semicolon can also be used if the two clauses are closely related: "The lecture was fascinating; it lasted for two hours."

2. Use a Comma and a Coordinating Conjunction (FANBOYS): Link the clauses with a comma plus one of the seven coordinating conjunctions: for, and, nor, but, or, yet, so. This defines the relationship. "The lecture was fascinating, but it lasted for two hours." (Contrast) or "The lecture was fascinating, so we took detailed notes." (Cause and effect).

3. Use a Subordinating Conjunction: Make one clause dependent on the other. This shows that one idea is more important than the other. "Although the lecture was fascinating, it lasted for two hours." Here, the focus is on its duration. "The lecture was fascinating because the professor was engaging." Here, the focus is on the fascination, with the reason being subordinate.

4. Restructure the Sentence: Sometimes the smoothest correction involves rephrasing. You might turn one clause into a phrase. "The fascinating lecture lasted for two hours."

The ACT Approach: Meaning and Context

On the ACT, these errors are embedded in passages. Your job isn't just to fix grammar; it's to choose the correction that best maintains the passage's style, tone, and logical flow. You must always consider the sentences before and after the error. A period might be grammatically correct, but if the author is building a rapid, connected argument, a semicolon or a conjunction might better preserve the intended rhythm and relationship between ideas.

For example, consider this comma splice in a passage about climate: "Arctic ice is melting at an unprecedented rate, this contributes to rising sea levels." The most effective fix isn't just grammatical; it's logical. Using a period is acceptable, but using "which" to create a dependent clause ("...rate, which contributes...") or a semicolon might better show the direct, causal connection the author is emphasizing. The correct answer will always be the one that is both grammatically sound and contextually appropriate.

Common Pitfalls

1. Misidentifying Long Phrases as Fragments: A sentence can be short ("Stop.") or very long with many descriptive phrases. As long as it has one subject and one predicate forming an independent thought, it's complete. Don't be fooled by complexity.
2. Overcorrecting with a Period: While using a period is never grammatically wrong when separating independent clauses, it can sometimes create a choppy, simplistic flow that goes against the author's sophisticated style. On the ACT, always check the other options to see if a conjunction or semicolon is a better fit for the context.
3. Forgetting the Comma Before FANBOYS: When joining two independent clauses with a coordinating conjunction, the comma before the conjunction is required. "The play was sold out so we went to a movie instead" is technically a run-on. The correct form is: "The play was sold out, so we went..."
4. Creating a New Error: When fixing one problem, ensure you don't introduce another. For instance, if you attach a fragment to an independent clause, check that the resulting sentence is logical. "She forgot her keys, which were on the table" works. "She forgot her keys, on the table" does not.

Summary

• A complete sentence must contain an independent clause with a subject and a predicate expressing a full thought.
• A fragment is an incomplete sentence; correct it by attaching it to a nearby independent clause or adding missing elements.
• A run-on sentence fuses independent clauses without proper punctuation; a comma splice joins them with only a comma.
• To fix run-ons and comma splices, use: 1) a period or semicolon, 2) a comma and a FANBOYS conjunction, 3) a subordinating conjunction to create a dependent clause, or 4) sentence restructuring.
• On the ACT, the best answer is always the one that is grammatically correct and best preserves the author's intended meaning, tone, and logical flow within the passage.