Why small errors cost you marks

You can have a genuinely insightful argument, a well-structured paragraph plan and a reading list that would impress your tutor, and still lose marks for a missing apostrophe. It feels unfair, but there is a logic behind it. Marking criteria in most UK universities reward clarity, precision and academic register, and grammar is how you demonstrate all three. When a sentence is grammatically shaky, the reader has to work harder to extract your meaning — and that friction is exactly what markers penalise.

What tends to cost students most is not the occasional typo but repeated patterns of error. A marker who spots three comma splices in an essay assumes the writer is unsure of the rule, not that they were in a hurry. The good news is that most academic grammar mistakes fall into a small number of categories. Learn the rules once and you will fix hundreds of sentences at a time.

Subject-verb agreement

Subject-verb agreement simply means that a singular subject takes a singular verb, and a plural subject takes a plural verb. It becomes tricky when words come between the two, or when a noun looks plural but isn't.

• The group of participants was recruited from three clinics. The subject is group, not participants, so the verb is singular.
• A number of studies suggest a link. Here a number of means several, so the verb is plural. But the number of studies has grown — the subject is now the number, which is singular.
• One of the most striking findings is the speed of the decline. The subject is one, so is, not are.
• Each of the interviews was transcribed. Words like each, every, either and neither are always singular.

Collective nouns — the government, the committee, the team — are a special case in British English. You may write the committee has decided or the committee have decided, depending on whether you think of it as one body or a group of individuals. Both are acceptable; inconsistency is not. Pick one approach and apply it throughout the essay.

Comma splices and run-on sentences

A comma splice happens when two complete sentences are joined with nothing but a comma. It is the single most common punctuation error in undergraduate writing.

Weak: The survey had a low response rate, this weakened the findings. Strong: The survey had a low response rate. This weakened the findings. Strong: The survey had a low response rate; this weakened the findings. Strong: The survey had a low response rate, and this weakened the findings.

Any of the three repairs works — a full stop, a semicolon, or a comma plus a coordinating conjunction (and, but, so, yet, for, nor, or). What you cannot do is use a comma alone.

Be careful with however, therefore and moreover. These are not conjunctions, so they cannot join two clauses with a comma. The sample was small, however, the results were consistent is wrong. Write The sample was small; however, the results were consistent or split the sentence in two.

Apostrophes: possession, not plurals

Apostrophes show that something belongs to someone, or that letters have been left out. They never make a word plural.

• Its is possessive; it's means it is. The same pattern applies to whose and who's.
• The student's argument was persuasive (one student). The students' arguments were persuasive (several students).
• Do not use an apostrophe for decades or numbers: the 1990s, not the 1990's. Equally, questionnaires were distributed, not questionnaire's.
• For singular nouns ending in s, most UK style guides prefer James's theory, though check your department's guide for consistency.

If you are unsure, ask yourself what the apostrophe is replacing. If the answer is "nothing", it probably does not belong there.

Three more traps worth checking

Dangling modifiers. Having reviewed the literature, the gap became clear suggests the gap did the reviewing. Rewrite: Having reviewed the literature, I identified a clear gap.

Inconsistent tense. Literature reviews sit in the present tense (Smith argues that...), while your own methods sit in the past (Data were collected...). Shifting between them mid-paragraph confuses the reader about what happened when.

Overly long sentences. If a sentence runs past three lines on the page, it is usually doing two jobs. Split it and your argument will read as more confident, not less.

How to proofread effectively

Most students proofread by rereading silently, which is the least effective method. Your brain fills in what it expects to see. Try these instead:

• Read the essay aloud. Comma splices and missing words become obvious when you have to say them.
• Read the last sentence first, then the second-last, and so on. This breaks the flow that hides errors.
• Check one issue at a time. Do a pass looking only at apostrophes, then a pass looking only at verb endings.
• Leave at least a day between finishing the draft and proofreading it, if your deadline allows.
• Keep a personal error list. Look back at your last three pieces of feedback. If apostrophes, agreement or comma splices come up more than once, that is your priority, not everything at once.

Grammar is not a separate skill bolted onto your subject knowledge — it is the mechanism by which that knowledge reaches your reader. Fixing these four or five habitual errors will lift the clarity of everything you write, and markers notice clarity immediately.