Complete SAT® Grammar and Punctuation Rules
Master all the essential grammar rules tested on the digital SAT. This comprehensive guide covers every punctuation mark, grammatical concept, and writing rule you need to know.
Updated for Digital SATKey Rule: Semicolon = Period
On the SAT, these two types of punctuation are considered identical, and you will never be asked to choose between them.
A. Between Two Complete Sentences
✓ Correct:
London is an old city. It has been inhabited for around 2,000 years.
✓ Correct:
London is an old city; it has many new buildings.
B. Before Conjunctive Adverbs
Use semicolons before conjunctive adverbs like however, therefore, or moreover at the beginning of a clause.
✓ Correct:
London is an old city; however, it has many new buildings.
✓ Correct:
London is an old city; therefore, it has buildings from many different eras.
Important Tip:
Make sure to read through every sentence all the way through to the period. Otherwise, you might not notice when there are two sentences.
Sentence Boundary Questions
Watch out for “sentence boundary” questions where the beginning of one sentence appears to be part of the previous sentence.
✗ Incorrect:
Barbara McClintock is a scientist whose discovery of “jumping” genes helped earn her the Nobel Prize in 1983, she won the award in Physiology or Medicine.
✓ Correct:
Barbara McClintock is a scientist whose discovery of “jumping” genes helped earn her the Nobel Prize. In 1983, she won the award in Physiology or Medicine.
Key Rule: Colon = Dash
Colons and single dashes are used to introduce lists and explanations. The SAT considers these grammatically identical and will never ask you to choose between them.
A. Before a List
✗ Incorrect:
London is home to a variety of: museums, castles, and shops.
✓ Correct:
Visitors to London often spend their time in three main types of attractions: museums, castles, and shops.
✓ Correct:
Visitors to London often spend their time in three main types of attractions—museums, castles, and shops.
B. Before an Explanation
✓ Correct:
When the Manchus took control of China, the Great Wall lost its protective purpose: the Chinese empire now extended well north of the wall, and its new enemies came from across the sea.
✓ Correct:
When the Manchus took control of China, the Great Wall lost its protective purpose—the Chinese empire now extended well north of the wall, and its new enemies came from across the sea.
Important:
A colon or dash must always follow a full sentence that makes sense as a complete thought and logically sets up the information that follows.
FANBOYS = For, And, Nor, But, Or, Yet, So
A comma + FANBOYS conjunction = Period = Semicolon
A. Comma + FANBOYS = Period = Semicolon
✓ Correct:
London is a very old city, but some parts of it are extremely modern.
✓ Correct:
London is a very old city, and it is very appealing to tourists.
B. Comma Splices
When two sentences are joined by a comma, the result is known as a comma splice. Comma splices are always incorrect.
✗ Incorrect:
London is a very old city, it has some extremely modern parts.
✓ Correct:
London is a very old city. It has some extremely modern parts.
Tip-off:
Look for comma + pronoun (e.g., it, they, s/he, one, you, I) - this often indicates a comma splice.
Dependent clauses cannot stand on their own as complete sentences.
They begin with subordinating conjunctions: although, because, when, until, while, since, before, and after.
Comma Rule for Dependent Clauses
When the dependent clause comes first, it must be followed by a comma.
✗ Incorrect:
Because London is a very old city it has buildings from many different eras.
✓ Correct:
Because London is a very old city, it has buildings from many different eras.
✓ Correct:
Although London is a very old city, it has many modern buildings.
Three Main Types of Transitions
Continuers
Add new and similar ideas, emphasize previous ideas, and convey sequence of events.
Examples: in addition, moreover, in fact, for example, and then
Cause-and-Effect
Indicate that an action or event is the result of a previous action/event.
Examples: therefore, consequently, thus
Contradictors
Signal opposing ideas.
Examples: however, nevertheless, in contrast
Strategy for Transition Questions
Cross out or ignore the transition and state the relationship between the sentences before checking the answers.
Example:
“The obvious reason for the construction of the Great Wall of China was protection. _________ China had no powerful enemies when the Wall began to be built.”
The two halves express opposing ideas, so a contradictor is needed: However
Non-essential information can be removed from a sentence without affecting its essential meaning.
It's like a little interruption. When the information between the commas is crossed out, the sentence still makes sense.
Three Ways to Punctuate Non-Essential Information
2 Commas
Most common punctuation type
London, which is a very old city, has some extremely modern parts.
2 Dashes
Grammatically identical to commas
London—which is a very old city—has some modern parts.
2 Parentheses
Also called “parenthetical” information
London (which is a very old city) has some modern parts.
Important:
Only one type of punctuation can be used—the options above cannot be mixed and matched. Many incorrect answers involve this error.
Two Correct Options Only
No commas (essential) OR Two commas, one before and one after (non-essential)
How to Determine Essential vs. Non-Essential
Read the sentence without the name/title and see if it still makes basic grammatical sense.
✗ Incorrect:
Researchers led by engineering professor, Vikram Iyer, have created a set of robotic devices...
Cross out: “Researchers led by engineering professor...have created” - doesn't make sense, so name is essential.
✓ Correct:
Researchers led by engineering professor Vikram Iyer have created a set of robotic devices...
Commas SHOULD be used:
A. To separate items in a list
Building muscle can boost metabolism, aid weight loss, and increase endurance.
B. To separate adjectives whose order could be reversed
Dinosaurs may have been active, warm-blooded animals.
Commas should NOT be used:
A. Before or after a preposition
Frida Kahlo is among the most famous artists of the twentieth century.
B. Between subjects and verbs
The oldest surviving bridge in London is Richmond Bridge, completed in 1777.
C. Before or after the word “that”
London is a city that has many old buildings and monuments.
Basic Rule: Apostrophe = Possessive, No apostrophe = Not possessive, plural only
A. Nouns
Singular nouns
Add apostrophe + -s
The cell's DNA
Regular plural nouns
Add -s or -es + apostrophe
The cells' DNA
Irregular plural nouns
Add apostrophe + -s
The people's responses
B. Pronouns
It's vs. Its
It's = it is | Its = possessive form of it
They're vs. Their vs. There
They're = they are | Their = possessive | There = a place
Pronouns are words that replace and refer back to nouns.
A. Singular-Plural Agreement: Pronouns
Singular
People = he or she | Things = it, its, itself
Plural
they, them, their, themselves
B. People vs. Things
✗ Incorrect:
Frida Kahlo was an artist which gained renown for her portraits.
✓ Correct:
Frida Kahlo was an artist who gained renown for her portraits.
Forming verbs: Singular 3rd person verbs end in -s, Plural 3rd person verbs do not end in -s
A. Compound subject (noun and noun) = Plural
✗ Incorrect:
The highly textured bark and distinctive silhouette of the Dutch Elm tree distinguishes it from the equally common English Elm tree.
✓ Correct:
The highly textured bark and distinctive silhouette of the Dutch Elm tree distinguish it from the equally common English Elm tree.
B. Prepositional Phrase
Prepositional phrases often distract from subject-verb disagreements.
✗ Incorrect:
Illegal logging in Mexican forests have resulted in the destruction of the monarch butterfly's habitat.
✓ Correct:
Illegal logging in Mexican forests has resulted in the destruction of the monarch butterfly's habitat.
Always keep verb tense consistent with other verbs in the paragraph.
A. Tense Consistency
✗ Incorrect:
Painter Frida Kahlo (1907-1954) earned renown for her portraits. She is strongly influenced by indigenous Mexican culture...
✓ Correct:
Painter Frida Kahlo (1907-1954) earned renown for her portraits. She was strongly influenced by indigenous Mexican culture...
B. Present Perfect vs. Simple Past
Present Perfect
has/have + verb (action beginning in past, continuing to present)
London and Paris have been tourist attractions for hundreds of years.
Simple Past
one-word past form (completed past action)
Rachel Carson published Silent Spring in 1962.
This comprehensive guide covers all 20 essential SAT grammar rules. Each rule includes detailed explanations, correct and incorrect examples, and important tips to help you master the digital SAT.