Comma Splices in a Lab Report
A student submits a lab report containing these sentences: (1) "The solution turned blue, this indicated a reaction." (2) "We measured the pH three times, the readings were 6.8, 6.9, and 6.8." (3) "The sample was heated, however it did not change color." (4) "Because the readings were consistent, we averaged them." The teacher marks (1)-(3) as comma splices but a classmate argues that (3) is fine because "however" is a conjunction. The student wants a rule they can apply without memorizing a list.
1. Explain why sentences (1)-(3) are problematic and why (4) is not, using a test the student can apply.
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Sentences (1) and (2) join two independent clauses - each could stand alone - with only a comma. Sentence (3) does the same: "The sample was heated" and "it did not change color" are both complete, and "however" is a conjunctive adverb, not a coordinating conjunction, so it cannot glue them with a comma. The classmate's premise is wrong.
Sentence (4) is correct because "Because the readings were consistent" is a dependent clause; it cannot stand alone, so the comma merely separates it from the main clause. The applicable test: cover everything before the comma and ask whether it is a complete sentence; then do the same after. Two complete sentences plus a comma is a splice. A dependent clause plus a main clause is fine. This test works without a list of words.
2. Give three different fixes for sentence (1) and explain how to choose among them.
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Fix A, a period: "The solution turned blue. This indicated a reaction." Fix B, a semicolon: "The solution turned blue; this indicated a reaction." Fix C, a subordinator: "The solution turned blue, which indicated a reaction" or "When the solution turned blue, this indicated a reaction."
Choose by meaning and rhythm. If the two ideas are tightly linked and equal in weight, a semicolon signals that link. If the second idea explains or results from the first, a subordinator such as "which" makes the relationship explicit. If the ideas are separate observations, a period is cleanest. In a lab report, precision about causal or temporal relations matters, so the subordinator is often the best choice; the period is never wrong but loses the connection. Avoid the common non-fix of adding a comma plus "and" when the logic is causal rather than additive.
3. How should the student revise sentence (3), and what general habit prevents this error?
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Options: "The sample was heated; however, it did not change color." Or "The sample was heated. However, it did not change color." Or restructure: "Although the sample was heated, it did not change color." Each respects the rule that "however" cannot join two independent clauses with a comma alone.
The preventive habit is to treat conjunctive adverbs - however, therefore, moreover, nevertheless - as signposts that require a semicolon or period before them and a comma after. A second habit: when a sentence contains a comma, check both sides for completeness before moving on. Proofreading specifically for comma-plus-pronoun or comma-plus-adverb patterns catches most splices, because those are the shapes where two complete thoughts most often get fused.