14 Punctuation Rules Examiners Actually Notice in a Thesis (2026)
Punctuation is the part of academic writing that supervisors comment on least and examiners notice most. A misplaced comma rarely changes a claim, but a page of them changes how carefully the reader believes the work was done. The rules below are the ones that recur in examiner reports and in professional copy-editing logs, ordered roughly by how often they appear. Each item gives the rule, the failure it prevents, and a search string you can run on your own draft tonight.
1. A comma cannot join two sentences
The comma splice is the single most common punctuation fault in postgraduate writing. The sample was small, the results should be treated with caution. Both halves are complete sentences, and a comma cannot hold them together.
Fix: use a full stop, a semicolon, or a conjunction — The sample was small, so the results should be treated with caution. Search tip: look for , however, , therefore, , thus and , this. Those four strings catch most splices, because conjunctive adverbs are not conjunctions.
2. However, therefore and moreover take a semicolon or a full stop
The effect was small; however, it was consistent across all three sites. Not The effect was small, however it was consistent. These words connect ideas without grammatically joining clauses, which is precisely why they cause splices.
Fix: semicolon before, comma after — or start a new sentence.
3. The semicolon has exactly two legitimate jobs
It joins two independent but closely related clauses, and it separates items in a list that already contains commas: Participants were recruited from Leeds, UK; Utrecht, the Netherlands; and Cork, Ireland.
Fix: if the material after your semicolon cannot stand as a sentence and is not a list item, you wanted a comma or a colon instead.
4. A colon needs a complete clause in front of it
The study measured three variables: motivation, engagement and attainment. Correct. The study measured: motivation, engagement and attainment. Incorrect — the colon has interrupted the verb from its object.
Search tip: search for are:, is:, were:, include: and such as:. Almost every hit is this error.
5. Hyphen, en dash and em dash are three different marks
The hyphen joins words: self-report measure, well-established finding. The en dash spans ranges and links equal partners: pp. 45–62, 2019–2024, the mind–body problem. The em dash marks a break in a sentence — like this one.
Fix: page and year ranges take an en dash, never a hyphen. This is one of the most visible faults in a reference list, because it repeats hundreds of times.
6. Hyphenate a compound modifier before a noun, not after
A well-validated instrument but the instrument is well validated. A long-term effect but the effect held in the long term. Adverbs ending in -ly never take the hyphen: a statistically significant difference, not a statistically-significant difference.
7. Restrictive and non-restrictive clauses take different punctuation
Commas change the meaning. The participants who completed all three sessions improved says only some participants improved. The participants, who completed all three sessions, improved says all of them did, and mentions in passing that they finished. In a results chapter this distinction is not cosmetic; it is the claim.
Fix: if removing the clause changes which things you are talking about, it is restrictive and takes no commas.
8. Apostrophes do not make plurals
The 1990s, not the 1990’s. Three PhDs, not three PhD’s. Two RCTs, not two RCT’s. The only apostrophes in a thesis mark possession or contraction — and contractions do not belong in formal academic prose anyway.
Search tip: search for ‘s preceded by a digit or by two capital letters. Every hit is wrong.
9. Its and it’s are not interchangeable
Its is possessive: the model and its assumptions. It’s is a contraction of it is, which should not appear in a thesis at all. So in practice, a thesis containing the string it’s almost always contains an error.
10. Quotation punctuation follows your variety, consistently
British convention normally uses single marks with doubles nested inside, placing terminal punctuation outside unless it belongs to the quotation. American convention uses doubles with singles inside and puts commas and full stops inside the closing mark. Both are correct; alternating between them is not. The wider set of variety differences is covered in our guide to choosing British or American English for your thesis.
11. Block quotations lose their quotation marks
Once a quotation is set as an indented block — APA 7 sets the threshold at 40 words — the indentation does the work and the quotation marks come off. Keeping both is redundant, and it is the commonest formatting error in a literature review.
Fix: also note that the citation goes after the closing full stop in a block quotation, and before it in a run-in quotation.
12. Ellipses mark omission, not hesitation
Three spaced or unspaced points show that you have cut material from inside a quotation. They are never a stylistic trailing-off in your own prose. Do not use an ellipsis at the start or end of a quotation unless the omission would otherwise mislead, and never use one to avoid finishing a thought.
13. Parentheses do not carry load-bearing content
A sentence must survive with the parenthetical material deleted. If your qualification is essential to the claim, it belongs in the main clause — the reader is entitled to assume that anything bracketed is optional. This matters most in a discussion, where a hedge parked inside brackets reads as an afterthought rather than a considered limit on the claim, a point that connects directly to how hedging and paragraph structure carry academic voice.
14. Abbreviations, Latin and the punctuation around them
e.g. and i.e. take full stops and are followed by a comma in American style; both are conventionally restricted to parentheses in formal prose, with for example and that is used in running text. et al. takes a full stop on al. only — et is a whole Latin word. cf. means compare, not see.
If your thesis is dense with initialisms, the front-matter conventions are set out in our guide to building a list of abbreviations.
The ten-minute punctuation sweep
- Search , however · , therefore · , thus · , this — comma splices.
- Search are: · is: · include: · such as: — broken colons.
- Search ‘s after digits or capitals — plural apostrophes.
- Search it’s — should be zero hits.
- Search – between two four-digit years — hyphens that should be en dashes.
- Search ly- — hyphens after -ly adverbs.
- Check every block quotation for stray quotation marks.
- Check that your serial-comma practice is identical in chapter one and chapter six.
Run this after the language-variety pass and before the final read, in the same sequence recommended in our thesis proofreading and self-editing checklist. Punctuation errors hide behind content errors; fix the content first and the punctuation becomes visible.
Why punctuation is a stance problem, not just a tidiness problem
Several of the rules above change meaning rather than appearance. The restrictive comma changes which participants you are describing. The parenthetical hedge changes how strongly you are committing to a finding. The colon before a list changes whether the list is an enumeration or an interruption. Punctuation is the last layer of the sentence, and it does the same work as the verb you chose to introduce a source — which is why it is worth reading alongside how reporting verbs signal your stance towards a citation.
Get the mechanics right from the first draft
Tesify writes in academic register and applies one consistent set of punctuation conventions across every chapter, so ranges, dashes, quotation marks and serial commas do not drift between the chapter you wrote in October and the one you wrote in March.
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Frequently Asked Questions
What is a comma splice and why does it matter in a thesis?
A comma splice joins two complete sentences with only a comma, as in The sample was small, the results are tentative. It matters because it is the most frequent punctuation error in postgraduate writing and it is trivially easy to find: search for , however, , therefore, , thus and , this.
When should I use a semicolon in academic writing?
Two cases only: to join two independent but closely related clauses, and to separate list items that already contain commas. If what follows your semicolon cannot stand alone as a sentence and is not a list item, you needed a comma or a colon.
What is the difference between a hyphen, an en dash and an em dash?
The hyphen joins words (self-report). The en dash spans ranges and links equal partners (pp. 45–62, the mind–body problem). The em dash marks a break in a sentence. Page and year ranges must take an en dash, which is the single most repeated dash error in reference lists.
Do I put quotation marks around a block quotation?
No. Once a quotation is indented as a block — APA 7 uses a 40-word threshold — the indentation signals the quotation and the marks are removed. The citation also moves after the closing full stop, rather than before it as in a run-in quotation.
Is it “the 1990s” or “the 1990’s”?
The 1990s. Apostrophes mark possession or contraction, never plurality. The same applies to initialisms: three RCTs, two PhDs. Search your draft for an apostrophe preceded by a digit or by two capital letters — every hit is an error.
Should I use the serial comma in a thesis?
American styles including APA and Chicago require it; British usage treats it as optional, though Oxford style uses it. The choice matters far less than consistency — mixed serial-comma practice across chapters is one of the clearest signs that a thesis was never harmonised.
Can I use “e.g.” and “i.e.” in the body of a thesis?
Conventionally they are restricted to parentheses, with for example and that is used in running text. Both take full stops on each letter. et al. takes a full stop only on al., because et is a complete Latin word.
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