Grammar Rules for Writing an Essay: A Guide to Polished, Persuasive Work
Strong essay grammar rests on complete sentences, agreeing subjects and verbs, correct commas and end punctuation, consistent tense, and accurate adjectives and adverbs. Check each layer in order during proofreading; fix fragments, run-ons, comma splices, agreement slips, and unnecessary tense shifts before you turn the draft in.
Build Complete Sentences First
A sentence is a group of words, usually containing a subject and a verb, that expresses a statement, question, instruction, or exclamation. In writing it starts with a capital letter and ends with a period or another end mark, as the Cambridge Dictionary defines it. Before you worry about elegant phrasing, make sure each line can stand on its own as a complete thought.
Grammar problems at the sentence level usually fall into three patterns: fragments, comma splices, and run-on (fused) sentences. The Purdue OWL clauses guide separates an independent clause, which has a subject and verb and expresses a complete thought, from a dependent clause, which has a subject and verb but cannot stand alone. Once you can tell them apart, each error has a predictable fix.
Fix Sentence Fragments
A fragment treats a dependent clause or an incomplete thought as if it were a full sentence. It may lack a subject, lack a working verb, or start with a word such as because, when, or although that leaves the idea unfinished. For example, "Because I forgot the exam was today" does not say what happened; it is a fragment even though it contains a subject and a verb.
You can repair a fragment by attaching it to a nearby independent clause or by adding the missing piece. "Because I forgot the exam was today, I did not study" completes the thought, and "I forgot the exam was today" works as its own sentence. When you proofread, read each sentence alone: if it does not answer who did what, it probably needs to be joined or completed.
Fix Comma Splices and Run-On Sentences
A comma splice joins two independent clauses with only a comma. "I like this class, it is very interesting" is a splice because both sides can stand alone. A run-on (fused) sentence joins two independent clauses with no punctuation at all, as in "My professor is intelligent I have learned a lot from her."
The clauses guide offers four fixes: replace the comma with a period and make two sentences; use a semicolon between closely related clauses; add a coordinating conjunction after the comma, as in "I like this class, and it is very interesting"; or turn one clause into a dependent clause with a word such as because. Choose the period when the ideas are separate, and the semicolon when they are tightly linked.
Make Subjects and Verbs Agree
Subjects and verbs must match in number: a singular subject takes a singular verb, and a plural subject takes a plural verb. The Purdue OWL agreement guide lists the cases that trip writers up, because the true subject is not always the noun closest to the verb.
Tricky Agreement Cases
Two or more subjects joined by and usually take a plural verb: "She and her friends are at the fair." When singular subjects are joined by or or nor, use a singular verb ("The book or the pen is in the drawer"), and when a singular and a plural subject are paired by or or nor, the verb agrees with the nearer noun: "The boy or his friends run every day," but "His friends or the boy runs every day."
Words such as each, everyone, everybody, somebody, nobody, and anyone are singular and take a singular verb even when they feel plural: "Everybody knows Mr. Jones." A phrase inserted between the subject and verb does not change the subject's number. In "One of the boxes is open," the subject is one, not boxes, so the verb stays singular. Collective nouns such as team, committee, and family usually take a singular verb in American English, and in sentences beginning with there is or there are, the verb agrees with the noun that follows: "There are many questions," but "There is a question."
Punctuate Clearly: Commas, Periods, and Semicolons
Punctuation tells readers where to pause, what belongs together, and when a thought ends. Most essay errors come down to a handful of comma decisions rather than obscure marks.
The Four Most Useful Comma Rules
The Purdue OWL comma guide gives four rules that cover most student writing. First, use a comma before a coordinating conjunction (and, but, for, or, nor, so, yet) that joins two independent clauses: "We wanted to stay at the mall longer, but the stores had closed." Second, place a comma after an introductory clause, phrase, or word that comes before the main clause: "After the dance, we went to get ice cream."
Third, use a pair of commas to set off nonessential information that can be removed without changing the core sentence; do not use commas around an essential that clause. Fourth, separate three or more items in a series with commas, including the Oxford comma when it prevents confusion. These rules handle lists, introductions, and joined clauses without over-punctuating every pause.
Periods, Question Marks, Exclamation Points, and Semicolons
Use a period to end a statement, a question mark to end a direct question, and an exclamation point only for genuine emphasis; essays rarely need more than one. A semicolon connects two closely related independent clauses that you do not want to split into short sentences: "To err is human; to forgive, divine." A colon introduces a list or explanation that follows a complete statement, but it should not sit directly after a verb.
Choose Nouns, Pronouns, Adjectives, and Adverbs Correctly
Word choice errors are subtler than agreement slips because the sentence still reads normally. Two areas cause most trouble: keeping nouns and pronouns consistent, and telling adjectives from adverbs.
Nouns and Pronouns
Capitalize proper nouns, the names of specific people, places, and organizations. Match each pronoun to its antecedent in number and gender, and keep the point of view you chose across the essay: do not drift from first person to third person in the same paragraph. The point of view guide walks through choosing among first, second, and third person and staying consistent.
Adjectives Versus Adverbs
The Purdue OWL adjective guide states the core rule: adjectives modify nouns, while adverbs modify verbs, adjectives, or other adverbs. "Richard is careless" uses an adjective to describe Richard; "Richard talks carelessly" uses an adverb to describe how he talks. Do not force an adverb next to every verb; placement depends on what the word modifies.
After a form of be and after sense verbs such as feel, taste, smell, sound, look, and seem, use an adjective to describe the subject. This is why "I feel bad" is correct when you mean upset or unwell; "feel badly" would suggest your sense of touch is poor. Good is an adjective and well is usually an adverb, though well also means in good health after a sense verb.
Keep Verb Tense Consistent
Establish one primary tense for the main part of your essay and shift only when the time frame genuinely changes. The Purdue OWL tense guide warns against unnecessary shifts: "Yesterday we walk to school but later rode the bus home" mixes present and past for one past event and should read "Yesterday we walked to school but later rode the bus home."
Use present tense for facts, for your own analysis, and when discussing events inside a literary work; use past tense to narrate events or describe historical actions. A deliberate shift is fine when it marks a real change in time, as in "The children love their new tree house, which they built themselves," where present states meet a past action. The problem is shifting without a reason, which makes readers lose the timeline.
The Preposition Myth: Ending a Sentence With a Preposition
You may have been told never to end a sentence with a preposition such as with, of, or to. That rule is not a real grammar rule. As Merriam-Webster explains, ending a sentence with a preposition is permissible in English; the ban traces to writers such as Poole and Dryden who tried to align English with Latin, where sentences cannot end in prepositions, and usage guides have near-unanimously rejected it for about a hundred years.
That does not mean you can never reword. In highly formal writing, or when a teacher prefers it, you may recast "I am looking for the book on the table" to sound smoother, but a natural terminal preposition is not an error and should not make you mangle a clear sentence. Treat it as a style choice, not a grammar test.
Proofreading Checklist for Your Next Essay
Run through this list in order before you turn the draft in:
- Every sentence has a subject and a verb and expresses a complete thought.
- No fragment stands alone; every comma splice and run-on is fixed with a period, semicolon, conjunction, or dependent marker.
- Each verb agrees with its true subject after you set aside inserted phrases.
- Commas follow the four rules; end punctuation and semicolons are used correctly.
- Pronouns match their antecedent, and the point of view stays consistent.
- Adjectives and adverbs modify the right word, especially after be and sense verbs.
- One primary tense holds, with shifts only for a real change in time.
- No sentence was mangled just to avoid a terminal preposition.
Grammar also works at the paragraph level: check that each paragraph carries one idea and that sentences connect smoothly. The essay paragraph guide covers how paragraphs build an argument from introduction to conclusion.
Pick one paragraph, run the checklist on it, and circle the rule you missed most often. When you want that practice built around your own writing, you can create a short interactive course on the grammar points you need, and work through a lesson before your next deadline.
Sources and review
Cambridge Dictionary — sentence (accessed 2026-10-22). Definition of a sentence as a subject-and-verb word group expressing a statement, question, instruction, or exclamation.
Purdue OWL — Independent and Dependent Clauses (accessed 2026-10-22). Independent and dependent clauses, fragments, comma splices, and fused sentences.
Purdue OWL — Subject/Verb Agreement (accessed 2026-10-22). Agreement guidelines for compound subjects, or/nor, indefinite pronouns, intervening phrases, and collective nouns.
Purdue OWL — Commas: Quick Rules (accessed 2026-10-22). Coordinating conjunctions, introductions, nonessential elements, and series commas.
Purdue OWL — Adjective or Adverb? (accessed 2026-10-22). What adjectives and adverbs modify, be and sense verbs, and good/well.
Purdue OWL — Verb Tense Consistency (accessed 2026-10-22). One primary tense and deliberate, time-based shifts.
Merriam-Webster — Can you end a sentence with a preposition? (accessed 2026-10-22). Usage history of the terminal-preposition ban and why it is not an error.