English grammar can seem endless, but most of it rests on a set of core rules. If you understand these, you can build correct sentences in almost any situation.
This guide is a quick-reference list of 20 core English grammar rules, each with a short explanation and example. Save it for revision before exams.
Sentence Rules
- Every sentence needs a subject and a verb. Birds fly.
- Normal word order is subject–verb–object. Rina reads books.
- Start with a capital letter and end with a full stop, question mark or exclamation mark.
- Join two complete sentences with a conjunction or a semicolon, not just a comma.
Verb Rules
- The verb agrees with the subject. She plays; they play.
- Use the present simple for habits and facts. Water boils at 100°C.
- Use the present continuous for actions happening now. I am reading.
- Use the past simple with finished time words. I went yesterday.
- Use the present perfect for experiences and results now. I have finished.
- After modal verbs, use the base verb. She can swim (not can swims).
For all tense forms, see our guide to the 12 English tenses.
Noun and Article Rules
- Use a/an with singular countable nouns mentioned for the first time. I saw a dog.
- Use the for something specific or already known. The dog was big.
- Uncountable nouns have no plural and no a/an. information, advice, water
- Use an before a vowel sound. an hour, a university
Pronoun Rules
- Use subject pronouns before verbs and object pronouns after verbs and prepositions. She saw me. Between you and me.
- Its = belonging to it; it’s = it is.
Adjective and Adverb Rules
- Adjectives describe nouns; adverbs describe verbs. a quick runner; she runs quickly.
- Use comparatives for two things and superlatives for three or more. taller / the tallest
Clause and Voice Rules
- Put a comma after a dependent clause that starts a sentence. If it rains, we will stay home.
- The passive uses be + past participle. The letter was written.
Learn more about these in clauses and active and passive voice.
Free Resources
Check each rule in more depth with Purdue OWL’s grammar guide, practise with its exercises and the British Council’s LearnEnglish lessons.
Final Thoughts
These 20 rules cover the core of English grammar. Learn them well, practise with examples, and you will have a strong base for every other grammar topic.
