How to Avoid Common Grammar Mistakes in a Thesis or Dissertation

Grammar mistakes in a thesis or dissertation rarely cause outright rejection on their own, but they accumulate. Examiners read hundreds of pages; repeated errors in subject–verb agreement, article use, tense, and punctuation signal carelessness and distract from your research contribution. The good news is that thesis grammar problems are highly predictable. The same dozen error types appear in draft after draft across disciplines. This guide identifies the most common grammar mistakes in long-form academic writing and shows you exactly how to find and fix them before submission.

Subject–verb agreement in long sentences

Complex academic sentences often separate the subject from its verb with clauses, citations, and parenthetical phrases. Writers lose track of whether the subject is singular or plural. Error: 'The group of participants were surveyed.' Fix: 'The group of participants was surveyed'—the subject is 'group,' not 'participants.' When in doubt, strip the sentence to its core subject and verb before adding modifiers back.

Tense inconsistency across sections

Each thesis section has conventional tense usage. Literature reviews summarise existing work in present tense: 'Jones (2023) demonstrates.' Methodology describes what you did in past tense: 'Data were collected between March and June 2025.' Results report findings in past tense: 'Scores improved significantly.' Switching tenses within a paragraph without reason is jarring. Create a tense map for your document and audit each chapter against it.

Article errors: a, an, the

Non-native English writers—and many native speakers—struggle with definite and indefinite articles. General rules help but academic usage has exceptions. Use 'the' when referring to something specific or previously mentioned: 'the questionnaire described in Section 3.2.' Omit articles with uncountable nouns used generally: 'Research suggests' not 'The research suggests' when speaking broadly. Proper nouns and abstract concepts in your field may not need articles at all—check published papers in your discipline for patterns.

Comma splices and run-on sentences

Joining two independent clauses with only a comma is a comma splice: 'The results were significant, the sample size was small.' Fix options include using a semicolon, adding a coordinating conjunction ('and,' 'but'), or splitting into two sentences. Run-on sentences omit necessary punctuation entirely. Both errors increase in frequency when writers rush to meet word counts or paste together draft fragments.

Misplaced and dangling modifiers

A dangling modifier does not clearly attach to the word it modifies. Error: 'Having analysed the data, the results were published.' Who analysed the data? The results did not analyse themselves. Fix: 'Having analysed the data, we published the results.' Place modifiers as close as possible to the words they describe.

Faulty parallelism in lists and comparisons

Items in a list or comparison must share the same grammatical form. Error: 'The study aims to measure attitudes, assessing behaviour, and it will evaluate outcomes.' Fix: 'The study aims to measure attitudes, assess behaviour, and evaluate outcomes.' Check every bulleted list in your methodology and every 'both…and' construction for parallel structure.

Pronoun reference and clarity

Ambiguous pronouns force readers to guess the antecedent. Error: 'When the supervisor reviewed the draft, it contained several errors.' Does 'it' refer to the review or the draft? Replace vague 'this,' 'it,' and 'they' with specific nouns when clarity fails. In formal academic writing, 'one' and passive constructions sometimes replace 'you,' but clarity always takes priority over rigid formality.

Which vs that

Use 'that' for restrictive clauses essential to meaning—no comma: 'The data that were excluded showed no pattern.' Use 'which' for non-restrictive clauses with commas: 'The full dataset, which included 500 responses, was cleaned before analysis.' American English distinguishes these; British English is more flexible, but consistency within your thesis matters more than regional preference.

Hyphenation and compound modifiers

Hyphenate compound adjectives before nouns: 'well-established theory,' 'cross-sectional design,' 'peer-reviewed journal.' Do not hyphenate after nouns or with -ly adverbs: 'the theory is well established,' 'a highly significant result.' Thesis writers often miss hyphens in methodological terms that appear dozens of times—create a personal hyphenation list for your field.

Capitalisation in headings and titles

Follow your style guide exactly. APA 7 uses sentence case for most headings: 'Data collection procedures.' Chicago and some university templates use title case: 'Data Collection Procedures.' Inconsistent capitalisation across chapters looks unprofessional. Set heading styles in Word or LaTeX once and apply them globally rather than formatting manually.

Numbers, units, and statistics

• Spell out numbers one through nine; use numerals for 10 and above (APA)—unless your guide differs.
• Always use numerals for statistics, percentages, scores, and dates.
• Include a space between number and unit: '25 kg' not '25kg.'
• Report p-values consistently: 'p < .05' or 'p = 0.03'—pick one format.

Common word confusions in academic prose

• Affect (verb) vs effect (noun)—'The intervention affected outcomes'; 'The effect was significant.'
• Fewer (countable) vs less (uncountable)—'fewer participants,' 'less time.'
• Complement vs compliment—'methods complement each other.'
• Principal vs principle—'principal component,' 'research principle.'
• Imply vs infer—authors imply; readers infer.

A practical grammar audit workflow

1. 1Run a grammar checker as a first pass—note recurring error types.
2. 2Search your document for known weak spots: 'which,' 'however,' 'due to the fact.'
3. 3Read one chapter aloud per day during final revision.
4. 4Ask a colleague to mark grammar issues without rewriting content.
5. 5Run a final proofread after all content changes are complete.

When grammar support is worth investing in

If grammar errors persist after multiple self-revision passes—especially under deadline pressure—professional academic editing targets the sentence-level patterns holding your thesis back. The goal is not to change your research but to ensure examiners engage with your findings instead of your comma usage.