Ten Punctuation Mistakes That Weaken Your Essay and How to Fix Them

Most essays are not marked down because of one stray comma. They lose marks because the punctuation makes the reader work harder than they should have to. A missing apostrophe signals carelessness; a comma splice blurs which idea belongs to which clause. Both are easy to fix once you know what to look for. Here are ten mistakes that turn up again and again in student writing, with the corrections that sort them out.

1. Comma splices: two sentences wearing one coat

A comma cannot join two complete sentences. When it tries, you have a comma splice:

The argument is persuasive, it relies on weak evidence.

The problem is not just grammatical. The reader has to decide how the two halves relate. Are they contrasting? Adding? Explaining? A comma splice leaves that relationship vague, and vague writing is weak writing. You have four dependable fixes:

Full stop. The argument is persuasive. It relies on weak evidence.
Semicolon. The argument is persuasive; it relies on weak evidence. Use this when the two halves are closely linked.
Coordinating conjunction. The argument is persuasive, but it relies on weak evidence.
Subordination. Although the argument is persuasive, it relies on weak evidence.

Watch out for conjunctive adverbs such as however, therefore and moreover. They do not fix a comma splice by themselves. The argument is persuasive, however, it relies on weak evidence is still wrong. Use a semicolon or a full stop: The argument is persuasive; however, it relies on weak evidence.

Read the passage aloud. If your voice drops in the middle, that drop is telling you where the sentence ends.

2. Apostrophes: three rules cover most cases

Possession

One owner, apostrophe before the s: the tutor's feedback. Several owners, apostrophe after: the tutors' feedback. Irregular plurals take the apostrophe before the s, as in children's or women's. Names ending in s cause arguments nobody wins — James's argument and James' argument are both in use, so pick one and stay consistent.

Plurals take no apostrophe

Three essays, the 1990s, two MPs, several hypotheses. The apostrophe in 1990's is wrong, and so is essay's when you simply mean more than one essay. The same rule applies to abbreviations: write three PhDs, not three PhD's.

Its and it's

It's is short for it is or it has. Its shows possession. The department published its findings. It's clear the findings were awkward. If you can substitute "it is", keep the apostrophe. If you cannot, remove it. The same logic applies to who's and whose: Who's responsible for the analysis? The team whose data was used.

Contractions and omissions

Apostrophes also mark missing letters in contractions: don't, can't, shouldn't. Academic writing often avoids contractions, but if you use them, punctuate them correctly. And remember that possessive pronouns never take apostrophes: yours, ours, theirs, hers, its.

3. Commas that quietly change your meaning

Some commas are optional. Others carry the entire sense of the sentence. Compare these:

Students who revise early write better essays.

Students, who revise early, write better essays.

The first sentence is about a particular group: only those students who revise early. The second claims that students in general revise early and write better essays — a very different assertion, and a much harder one to defend. The same logic explains the difference between My brother, who lives in Leeds, is a lecturer (I have one brother, and by the way he lives in Leeds) and My brother who lives in Leeds is a lecturer (I have more than one).

Introductory words and phrases also need a comma after them: However, the sample is small. In 2019, the policy changed. And watch the list that ends in ambiguity. She thanked her tutor, a novelist and a poet could mean three people or one multitalented person. Either add the serial comma or reword the sentence.

Two more comma traps are worth knowing. First, do not put a comma between a subject and its verb: The main problem with the essay, is its lack of focus is wrong. Second, use a comma before a coordinating conjunction only when it joins two independent clauses: The data was incomplete, and the conclusion was premature. If the second half is not a complete sentence, the comma usually goes: The data was incomplete and the conclusion premature.

4. Semicolons and colons: sharp tools, easily blunted

A semicolon joins two independent clauses that belong together: The evidence is thin; the conclusion is bold. Do not pair it with and, but or so — those conjunctions take a comma, or nothing at all.

A colon introduces something: a list, an explanation, a quotation. It must follow a complete clause, so The essay needs three things: a clear thesis, evidence and signposting works, while The essay needs: a clear thesis… does not. Slipping a colon between a verb and its object is the commonest colon error in student writing. Do not use a colon after such as, including or for example.

Semicolons also separate items in a complex list, especially when the items themselves contain commas: The panel included Dr. Shah, a sociologist; Professor Ali, an economist; and Dr. Jones, a historian. Without the semicolons, the reader cannot tell where one item ends and the next begins.

5. Hyphens, dashes and ellipses

These three marks look similar and do entirely different jobs.

Hyphen (-) joins words: a well-argued case, nineteenth-century fiction, a two-year study. Once the phrase follows the noun, the hyphen usually goes: the case was well argued.
En dash (–) marks ranges: pages 45–52, 1990–2000.
Em dash (—) or spaced en dash marks a break in thought — like this — and should be used sparingly. Choose one style and apply it throughout.
Ellipsis (…) shows omitted words, usually in quotations: The report claims that "the evidence … remains inconclusive." Do not use it as a casual pause in academic prose. If you omit material, make sure the meaning is not distorted.

A hyphen is not a dash. A hyphen joins; a dash separates. If you can replace the mark with "to" or "through", you probably want an en dash. If you can replace it with a stronger pause than a comma, you probably want a dash. Ellipses are for quotations, not for suspense.

6. Quotation marks: punctuation inside or outside?

Quotation marks

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