Grammar foundations
Before any punctuation or grammar rule makes sense, you need to see the structure underneath a sentence. Almost every rule on the SAT and ACT is really one question — "what kind of pieces am I joining, and are they complete?" This note builds the tools to answer it: the parts of speech, grouping words into phrases and clauses, finding the subject and verb at a sentence's core, and telling independent from dependent clauses.
"Put a semicolon between two independent clauses." "Don't put a comma between a subject and its verb." "A colon needs a complete sentence before it." Every one of these rules names a structure — clause, subject, verb, complete sentence. If you can't spot those structures, the rules are just words. This note teaches you to spot them.
Part 1 · The Building Blocks
The parts of speech
Words do jobs. The "part of speech" is just the job a word is doing in its sentence — and the same word can do different jobs in different sentences. For the tests, you don't need all the grammar vocabulary; you need to recognize these eight well enough to find the important ones (nouns and verbs) fast.
| Part of speech | Its job | Examples |
|---|---|---|
| Noun | Names a person, place, thing, or idea | scientist, harbor, telescope, freedom |
| Pronoun | Stands in for a noun | she, it, they, who, this |
| Verb | Shows an action or a state of being | build, discovered, is, seems |
| Adjective | Describes a noun | ancient, bright, careful |
| Adverb | Describes a verb, adjective, or other adverb | quickly, very, often |
| Preposition | Shows relationship (place, time, direction) | in, on, after, between, of |
| Conjunction | Connects words or groups of words | and, but, because, although |
| Interjection | Expresses emotion (rare on tests) | oh, wow, hey |
The two that matter most: nouns and verbs are the load-bearing words. Every sentence is built around a noun doing something (the subject) and the something it does (the verb). Your first move on any test sentence is to find these two — everything else hangs off that frame.
A closer look at verbs: action vs. linking
Most verbs show action (run, write, collapse). A smaller set are linking verbs — they don't show action; they connect the subject to a description. The big one is to be (is, are, was, were, been), plus sense verbs like seem, become, appear, feel.
The engineer tested the bridge. — action
The bridge was unstable. — linking (connects bridge → unstable)
Why it matters: linking verbs are easy to miss because they feel like small words. But is/are/was/were are still the main verb of their clause — and a clause needs one. Forgetting that a linking verb "counts" is a common reason students mislabel a complete sentence as a fragment.
A closer look at prepositions
A preposition starts a prepositional phrase — a preposition plus its object (in the harbor, after the storm, of the city). These phrases are everywhere, and they are the test's favorite way to hide the real subject. The subject of a sentence is never inside a prepositional phrase. Learning to spot and mentally bracket these phrases is half the battle for subject-verb agreement.
The crates (of fresh fruit) (from the southern farms) were unloaded.
subject verb prepositional phrase
Bracket the two prepositional phrases and the sentence shrinks to crates … were. The subject is crates (plural) — not fruit or farms, which only sit closer to the verb to trick you.
Part 2 · From Words to Structures
Phrases vs. clauses
Once you can spot parts of speech, the next move is to see how words group. There are only two kinds of groups that matter, and the entire punctuation system depends on telling them apart.
across the frozen lake — phrase (no subject, no verb)
running out of time — phrase (verb-ish word, but no subject)
the skaters crossed the frozen lake — clause (subject + verb)
we were running out of time — clause (subject + verb)
The test that drives everything: ask of any word group — does it have its own subject doing its own verb? No → it's a phrase. Yes → it's a clause. This single question is the foundation of every comma, semicolon, colon, and dash rule you'll meet.
Part 3 · Finding the Core
Identifying the subject and verb
The skill that unlocks the most points is stripping a long sentence down to its core — the main subject and main verb. The tests bury that core under prepositional phrases, descriptions, and extra clauses. Here's the reliable order of operations.
The collection (of rare maps) (in the university's archive) has grown.
subject verb prepositional phrase
Bracket (of rare maps) and (in the university's archive). Core: collection has — singular subject, singular verb. The nearby plurals maps and the possessive university's are bait.
Reading a test sentence left to right, you get pulled along by every phrase and lose the thread. Bracketing — even rough, in your head — forces you to step back and see the skeleton: one subject, one verb, and a few modifiers hanging off them. Once you see the skeleton, you can tell instantly whether the sentence is complete, where one clause ends and another begins, and what punctuation belongs between them.
Part 4 · The Distinction That Powers the Rules
Independent vs. dependent clauses
Both are clauses — both have a subject and verb. The difference is whether the clause can stand on its own as a sentence.
The harbor froze. — independent: complete sentence.Because the harbor froze. — dependent: now a fragment.Because the harbor froze, the ships stayed in port. — dependent + independent: complete.The word because didn't change the subject or verb — it changed the clause's ability to stand alone. That's the entire concept.
If a clause begins with one of these, it's dependent and cannot stand alone: after, although, as, because, before, even though, if, since, that, though, unless, until, when, whereas, which, while, who. Memorizing this short list lets you label any clause on sight.
Putting it together: reading a whole sentence
Here's the entire toolkit applied to one sentence — the exact mental process to run on a test question.
Although the storm had passed, the crew (on the damaged ship) remained alert.
subject verb dependent clause / phrase
- Dependent clause: Although the storm had passed — starts with although, can't stand alone.
- Prepositional phrase: (on the damaged ship) — bracket it; the subject isn't in here.
- Core: crew remained — singular subject, singular verb. The independent clause.
Now the punctuation makes sense: the dependent clause comes first, so it's followed by a comma. You didn't memorize that — you saw it.
How this maps onto the rules
Everything you just learned points straight at the rules you'll apply on test day. A preview of the payoff:
| When you see… | The rule that applies |
|---|---|
| Two independent clauses | Join with a period, semicolon, or comma + FANBOYS — never a comma alone. |
| A dependent clause first | Follow it with a comma. |
| A subject and its verb | Never separate them with punctuation; make them agree in number. |
| An opening phrase + comma | The noun right after must be what the phrase describes (or it dangles). |
| A complete sentence before a colon | The colon can introduce a list or explanation. |
You now have the structural vocabulary the rules are written in. To see these structures drawn out, the Sentence Diagramming note turns each into a picture. For the full set of punctuation and grammar rules with worked examples, see the Grammar & Punctuation Rules Reference.