Grammar isn't a set of arbitrary rules to trip you up — it's the shared system that lets your writing be understood exactly as you mean it. You already use most of it without thinking. This lesson names the key parts so you can spot mistakes, fix them, and write sentences that are clear and correct.
Every word in a sentence does a job. A noun names a thing (dog, city, freedom). A verb is an action or a state of being (run, is, think). An adjective describes a noun (a red car), and an adverb describes a verb, often telling how (she ran quickly).
A few more do the connecting work: pronouns stand in for nouns (he, she, it, they), prepositions show position or relationship (in, on, under, before), and conjunctions join things (and, but, because). You don't need to label every word — but knowing these lets you talk about, and fix, what a sentence is doing.
A complete sentence needs two things: a subject (who or what the sentence is about) and a verb (what they do or are). 'The dog barked' is a sentence — subject *dog*, verb *barked*. 'The dog in the yard' is not a sentence, because there's no verb telling us what the dog did.
A group of words missing a subject or a verb is a fragment, and it usually reads as incomplete. When you check your writing, make sure each sentence has both a subject and a verb and expresses a full thought.
The verb has to match the subject in number. A singular subject takes a singular verb (The dog runs); a plural subject takes a plural verb (The dogs run). This trips people up when words come between the subject and the verb — the verb still matches the real subject, not the nearest noun.
In 'The box of old photos is heavy', the subject is *box* (singular), so it's *is*, not *are* — even though *photos* sits right next to the verb. Find the true subject first, then match.
A few punctuation rules fix most errors. Use a full stop to end a complete sentence. Don't join two full sentences with only a comma — that's a *comma splice* ('It was late, I went home'). Instead use a full stop, a semicolon, or a comma plus a joining word ('It was late, so I went home').
The apostrophe does two jobs: it shows possession (the dog's bowl) and marks missing letters in a contraction (do not → don't). A classic mix-up is *its* (belonging to it) versus *it's* (it is) — 'its' has no apostrophe when it means belonging, just like *his* and *hers*.
Try these. Pick an answer to see whether it's right and why.