Common grammar mistakes in academic writing, and how to fix them

The grammar slips that appear most often in theses and journal articles, with simple ways to spot and correct them.

Good research can be hidden behind small grammar slips. Most of them are easy to fix once you know what to look for. These are the mistakes we see most often in theses, dissertations and journal articles, with a simple way to correct each one.

Comma splices

A comma alone cannot join two complete sentences. “The sample was small, the results were not significant” has two clauses, and they need a full stop, a semicolon or a linking word. Try: “The sample was small, so the results were not significant.” Read each comma and ask whether a full sentence sits on both sides of it.

Misplaced “only” and “almost”

Words such as “only” and “almost” change meaning depending on where they sit. “We only measured three variables” suggests you did nothing else. “We measured only three variables” says the number is three. Place the word directly before the item it limits.

Subject and verb agreement

Long phrases between the subject and the verb can confuse the verb. In “The effect of the two treatments on the outcomes were significant”, the subject is “effect”, so the verb should be “was”. Remove the phrase in the middle to find the true subject, then choose the verb to match it.

Tense consistency

Use the past tense for the work you carried out, such as “Participants completed the survey.” Use the present tense for established facts and for what a table shows, such as “Table 2 shows a clear trend.” Keep the tense steady within each section, and check that the methods and results follow the same pattern.

Articles: a, an and the

Articles are hard for many writers, especially if their first language has none. Use “the” for a specific item the reader already knows, such as “the study” that you have described. Use “a” or “an” for a general item, such as “a study of this kind”.

“Which” and “that”

Use “which”, with a comma before it, for extra information that could be removed without changing the sentence. Use “that” for information the sentence needs. “The method, which was piloted in 2024, proved reliable” adds a detail. “The method that was piloted in 2024 proved reliable” tells the reader which method you mean.

Hedging your claims

Match the strength of your verb to the strength of your evidence. “Shows” suits direct evidence. “Suggests” or “may” suits a possible explanation. Overstating a finding is a common reason reviewers ask for revisions.

Takeaways

• Check every comma that joins two clauses
• Place “only” directly before the word it limits
• Find the true subject before you choose the verb
• Keep tenses consistent within each section
• Read your work aloud to catch missing words

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