The Complete Academic Grammar Guide for 2026

Grammar errors in academic essays don't just lose points — they undermine the argument you worked hard to build. A reader distracted by a comma splice or a dangling modifier stops engaging with your ideas and starts noticing your mistakes. This guide covers the 9 most common grammar errors found in college and graduate-level writing, with specific examples and correction strategies for each.

1. Comma Splice

A comma splice is one of the most commonly penalized errors in academic writing. It happens when two complete sentences (independent clauses) are joined only by a comma, with no coordinating conjunction.

Why it matters in academic writing

In casual or creative writing, comma splices sometimes appear intentionally for stylistic effect. In academic essays, they are almost always an error. Professors and markers who see comma splices typically dock points without comment — they're a signal of rushed proofreading.

How to fix it

• Split into two separate sentences with a period.
• Add a coordinating conjunction (for, and, nor, but, or, yet, so) after the comma.
• Replace the comma with a semicolon if the two clauses are closely related in meaning.
• Use a subordinating conjunction to make one clause dependent: "Although the experiment ran for six weeks, the data showed a clear trend."

2. Subject-Verb Agreement

Subject-verb agreement errors occur when the subject and verb in a sentence don't match in number — a singular subject with a plural verb, or vice versa. These are especially tricky in academic writing because long noun phrases often separate the subject from its verb.

In the example above, the subject is "impact" (singular), not "discourse" or "media." The prepositional phrase in between creates distance that makes writers default to a plural verb by mistake.

Common traps

• Collective nouns: "The committee decides" (singular) vs "The members decide" (plural)
• Indefinite pronouns: "Everyone is" not "Everyone are" — words like everyone, nobody, someone are always singular.
• Either/or constructions: the verb agrees with the closer subject — "Neither the students nor the professor was present."
• Data: academic usage increasingly treats "data" as plural — "The data suggest" rather than "The data suggests."

3. Tense Consistency

Academic essays should maintain a consistent tense throughout. Unexplained tense shifts — switching from past to present or vice versa mid-paragraph — are a common error in student writing, especially in longer essays where the writer loses track of their starting tense.

Tense conventions in academic writing

• Use present tense when discussing what a text, author, or theory argues or claims.
• Use past tense when describing what you or another researcher did in a study.
• Use present perfect when describing research that is still relevant: "Researchers have found…"
• Stay consistent within each section and signal any intentional shifts clearly.

4. Dangling Modifiers

A dangling modifier is a word or phrase that's supposed to modify a noun but doesn't attach correctly to the word it's modifying. In academic writing, they often appear in sentences that begin with participial phrases.

The wrong version implies that "several gaps" reviewed the literature. The fix is to ensure the subject of the main clause is the one performing the action described in the opening phrase.

5. Passive Voice Overuse

Passive voice is not always incorrect in academic writing — some disciplines, particularly the sciences, prefer it. But overusing passive constructions weakens argumentative force and often produces wordier, vaguer sentences.

6. Apostrophe Errors

Apostrophe misuse falls into two categories: using an apostrophe where it shouldn't be, and omitting it where it should appear. Both appear frequently in student essays.

Quick rules

• Plural nouns (no possession): no apostrophe — "students," "essays," "results."
• Possessive singular: add 's — "the researcher's conclusion."
• Possessive plural: add apostrophe after the s — "the researchers' conclusions."
• It's = it is. Its = possessive. Never "its'" — that doesn't exist.

7. Run-On Sentences

A run-on sentence occurs when two or more independent clauses are joined without any punctuation or conjunction. Unlike a comma splice (which at least has a comma), a run-on has nothing separating the clauses.

8. Academic Tone

Academic tone refers to the formal register expected in scholarly writing. Casual phrasing, contractions, colloquialisms, and hedging language that's too weak or too strong all affect tone score.

• Avoid contractions: "don't" → "do not," "it's" → "it is."
• Avoid colloquial phrases: "a lot of" → "a significant number of," "looks at" → "examines."
• Hedge appropriately: "This proves that…" is often too strong — "This suggests that…" is more academically appropriate.
• Avoid first-person where discipline norms discourage it — check your style guide or assignment instructions.
• Avoid starting sentences with "But" or "And" in formal academic writing — use "However," "Furthermore," or restructure the sentence.

9. Grammar Tips for ESL Academic Writers

Non-native English writers face a specific set of grammar challenges in academic essays. The following patterns show up most frequently and are specifically detected by the essay grammar checker's ESL-aware analysis.