Reading and Writing · Standard English Conventions

SAT Boundaries: The Complete Punctuation Guide

Boundaries questions test whether you can separate and join sentences, clauses, and phrases with the right punctuation. The questions look varied, but they all come from one skill: knowing whether the words on each side of a mark are complete sentences. This guide gives you the clause test, a table of every rule the SAT uses, and a method that makes punctuation choices fast and consistent.

Section: Reading and Writing
Domain: Standard English Conventions
Questions per test: about 6 to 8
Target time: 30 to 45 seconds each

What boundaries questions test

A boundaries question shows a one- or two-sentence passage with a blank or underlined section, and four choices that differ in punctuation (or sometimes in a connecting word). You are asked which choice conforms to the conventions of Standard English. Only one choice follows the rules; the others commit one of a small set of recurring errors.

The error types are consistent: a comma splice, a run-on, a fragment created by a stray period, a colon or semicolon in the wrong place, a missing or extra comma around a nonessential phrase, or a comma that wrongly separates a subject from its verb. Learn to recognize those six patterns and you can answer almost every question by rule rather than by feel.

The clause test and the four joining tools

Find the punctuation spot, then ask two questions. Is the group of words before it an independent clause? Is the group of words after it an independent clause? The answers tell you which marks are allowed.

The four ways to join two independent clauses (IC means independent clause)
Pattern	Example	Notes
IC. IC.	The lake froze early. The fishing season ended sooner.	Period: two separate sentences.
IC; IC.	The lake froze early; the fishing season ended sooner.	Semicolon: the clauses are closely related. No capital after the semicolon (unless a proper noun).
IC, FANBOYS IC.	The lake froze early, so the fishing season ended sooner.	Comma plus a coordinating conjunction (for, and, nor, but, or, yet, so).
IC: explanation.	The lake froze early: the autumn was unusually cold.	Colon, only if the second part explains, illustrates, or specifies the first. A dash can do the same job.

Any other way of joining two independent clauses is an error. A comma alone creates a comma splice. Nothing at all creates a run-on (also called a fused sentence). A comma plus a conjunctive adverb such as “however” or “therefore” is also a splice, because those words are not coordinating conjunctions.

Splices and run-ons versus fixes
Error	Example	Fix
Comma splice	The vote passed, the new rule begins Monday.	Replace the comma with a semicolon or period, or add a conjunction after the comma.
Run-on	The vote passed the new rule begins Monday.	Add a period, semicolon, or comma plus conjunction.
Splice with conjunctive adverb	The vote passed, however the rule begins Monday.	Use a semicolon before however and a comma after: “; however,”.

Every rule the SAT tests

Rules for commas
Rule	Correct example	Common error
Comma after an introductory element (dependent clause or phrase) before the main clause	Although the road was closed, the bus arrived on time.	Although the road was closed the bus arrived on time. (missing comma)
Comma plus FANBOYS between two independent clauses	The road was closed, but the bus arrived on time.	The road was closed but the bus arrived on time. (missing comma)
No comma before a conjunction joining two verbs (compound predicate)	The bus left the depot and reached the station.	The bus left the depot, and reached the station.
Commas between items in a series of three or more	She packed maps, a compass, and a flashlight.	She packed maps a compass and a flashlight.
Comma between coordinate adjectives (can be reordered or joined by “and”)	a long, difficult hike	a small, wooden box (the adjectives are not coordinate: you cannot say “wooden and small box” naturally)
No comma between subject and verb, or verb and object	The director of the program will announce the results.	The director of the program, will announce the results.
Commas around a nonessential element (paired)	Dr. Lopez, who studies glaciers, will speak tonight.	Dr. Lopez, who studies glaciers will speak tonight. (only one comma)
No commas around an essential element	The scientist who studies glaciers will speak tonight.	The scientist, who studies glaciers, will speak tonight. (when it identifies which scientist)

Rules for semicolons, colons, and dashes
Mark	Use	Correct example	Not allowed
Semicolon	Between two independent clauses	The team trained all summer; they won the title.	After a dependent clause: “Because they trained; they won.”
Semicolon	Between items in a series that already contain commas	We visited Austin, Texas; Denver, Colorado; and Reno, Nevada.	Between a subject and its verb
Colon	After an independent clause, to introduce an explanation, example, or list	She packed three things: maps, a compass, and a flashlight.	After a verb or preposition: “She packed: maps and a compass.”
Dash (single)	After an independent clause, to introduce an explanation or addition	The plan has one flaw—it costs too much.	Combined with a comma at the same break
Dashes (pair)	Around a nonessential element, in place of paired commas	The mayor—who ran unopposed—won easily.	A dash on one side and a comma on the other
Parentheses (pair)	Around nonessential information	The festival (held each June) draws thousands.	A single parenthesis

Conjunctive adverbs (however, therefore, moreover, for example) and how to punctuate them
Position	Pattern	Example
Between two independent clauses	IC; adverb, IC	The path was steep; however, the view was worth it.
Between two sentences	IC. Adverb, IC.	The path was steep. However, the view was worth it.
Inside a clause	subject, adverb, verb	The view, however, was worth it.
Not allowed	IC, adverb, IC	The path was steep, however, the view was worth it. (splice)

Apostrophes (possessives and contractions)
Situation	Rule	Example
Singular possessive	Add 's	the student's notes
Plural possessive (regular plural ending in s)	Add an apostrophe after the s	the students' notes
Irregular plural possessive	Add 's	the children's books
Simple plural	No apostrophe	the students arrived
Possessive pronouns	Never take an apostrophe	its, hers, theirs, ours, whose
Contractions	Apostrophe replaces letters	it's (it is), who's (who is), they're (they are)

Step-by-step method

Locate the boundary and look at what changes across the choices (period, semicolon, comma, colon, dash, none).
Test the left side: is it an independent clause? Mark it IC or not.
Test the right side: is it an independent clause? Mark it IC or not.
Apply the pattern. IC and IC: period, semicolon, comma plus FANBOYS, or colon (for explanation). IC and fragment: usually no mark, a comma, a colon, or a dash. Fragment and IC: comma after the introductory element.
Check paired marks. If an opening comma, dash, or parenthesis is already present, find its matching partner.
Check for a subject-verb split. If the mark sits between a subject and its verb (or a verb and its object), eliminate any single comma, semicolon, colon, or dash.
Reread the winner in the full sentence.

Fast decision table
Left of mark	Right of mark	Allowed marks
Independent clause	Independent clause	Period, semicolon, comma + FANBOYS, colon or dash (if explanation)
Independent clause	Dependent clause starting with because, although, which, etc.	Usually no mark or a comma (with some exceptions like “, which”)
Dependent clause or introductory phrase	Independent clause	Comma
Independent clause	List or word or phrase that explains it	Colon or dash
Subject	Verb	No mark (unless paired commas or dashes around an inserted element)
Verb or preposition	Object or list	No mark (never a colon)

Worked examples

Worked example

Example 1: introductory element (easy)

Although the committee had reviewed every proposal ______ it postponed its decision until the budget was confirmed.

Which choice completes the text so that it conforms to the conventions of Standard English?

Aproposal; it
Bproposal, it
Cproposal. It
Dproposal: it

Show the solution

Left side: “Although the committee had reviewed every proposal” begins with “although,” so it is a dependent clause, not an independent one.
Right side: “it postponed its decision…” is an independent clause.
A dependent clause followed by an independent clause takes a comma.
Choice A is wrong because a semicolon needs an independent clause on both sides. Choice C leaves “Although…proposal.” as a fragment. Choice D is wrong because a colon must follow a complete clause.
Choice B is correct.

Answer: B

Worked example

Example 2: paired punctuation around a nonessential phrase (medium)

Dr. Imani Okafor, a geologist who has studied the region for twenty years______ will lead the expedition.

Which choice completes the text so that it conforms to the conventions of Standard English?

A, will lead
B—will lead
C; will lead
D: will lead

Show the solution

The phrase “a geologist who has studied the region for twenty years” renames Dr. Okafor and can be removed without changing the sentence’s basic meaning, so it is nonessential.
A nonessential phrase is set off on both sides. The opening comma after “Okafor” is already there, so a matching comma is needed after “years.”
Choice B mixes a comma with a dash. Marks around one phrase must match.
Choices C and D insert a semicolon or colon between a subject and its verb, which is never allowed.
Choice A supplies the closing comma and is correct.

Answer: A

Worked example

Example 3: a colon after a verb (medium)

For the festival's craft booth, volunteers will need______ scissors, glue, and construction paper.

Which choice completes the text so that it conforms to the conventions of Standard English?

A: scissors
B; scissors
C, scissors
D scissors

Show the solution

The words before the blank, “For the festival's craft booth, volunteers will need,” do not form a complete sentence, because “need” still requires its object.
A colon must follow a complete independent clause, so choice A is wrong. A semicolon needs independent clauses on both sides, so B is wrong.
A comma would separate the verb “need” from its object, which is not allowed, so C is wrong.
With no punctuation, the verb flows into its object, and the commas in the list come only between the items. Choice D is correct.

Answer: D

Worked example

Example 4: conjunctive adverb (hard)

The study's sample was small______ its results were consistent across all three sites.

Which choice completes the text so that it conforms to the conventions of Standard English?

A, however its
B; however, its
C, however, its
D however, its

Show the solution

Left side: “The study's sample was small” is an independent clause. Right side: “its results were consistent across all three sites” is also an independent clause. “However” is a conjunctive adverb that links them.
Two independent clauses cannot be joined by a comma alone, and “however” is not a coordinating conjunction, so it does not fix the problem. That eliminates A and C (both comma splices) even though C looks neatly punctuated.
Choice D has no mark before “however,” so it is a run-on.
The correct pattern is a semicolon before the conjunctive adverb and a comma after it. Choice B is correct.

Answer: B

Common traps

What separates the hardest questions

Hard boundaries questions use the same rules, but they hide the structure. Expect these patterns.

Long inserted elements. A nonessential phrase with several words (or its own commas) sits between the subject and the verb. Remove it mentally to see whether the subject and verb need a mark between them. They do not.
Subordinate clauses after a semicolon. A semicolon followed by “because,” “although,” or “which” is wrong, because those words start dependent clauses.
Essential versus nonessential. “The poet Maya Angelou” takes no commas because the name identifies which poet. “Her mother, Ana,” takes commas when she has only one mother. Test whether removing the phrase would leave the noun unclear.
Dashes and colons that look similar. Both can follow an independent clause to introduce an explanation, but only dashes can also come in pairs. A colon cannot close a phrase.
Hidden compound predicates. “The team planned the trip, and booked the hotels” has no second subject, so the comma is an error.
Choice sets that fix one thing and break another. A choice may correct the semicolon but leave a missing comma after “however.” Check every mark, not only the first.

Timing and practice plan

Boundaries questions should take 30 to 45 seconds. If a question takes longer, you are probably reading for sound rather than applying the clause test.

Day 1: learn the four ways to join independent clauses and write two original sentences for each.
Day 2: do ten untimed questions and label every clause IC or not before choosing.
Day 3: drill nonessential elements. Write five sentences with paired commas, then five with paired dashes.
Day 4: drill “however,” “therefore,” and other conjunctive adverbs. Practice the “; adverb,” pattern until it is automatic.
Day 5: do a timed set of fifteen questions at about 40 seconds each. For every miss, write the rule you broke.
Ongoing: keep a one-line rule log. Review it before each practice session.

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Every rule the SAT tests
Step-by-step method
Worked examples
Common traps
What separates the hardest questions

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Boundaries: FAQ

What are boundaries questions on the SAT?

They are Standard English Conventions questions about punctuation and sentence structure, such as where to put commas, semicolons, colons, dashes, and periods between clauses and phrases.

How do I fix a comma splice on the SAT?

Replace the comma with a period or semicolon, or keep the comma and add a coordinating conjunction such as and, but, or so. A comma plus however is still a splice.

When do you use a semicolon on the SAT?

Use a semicolon between two independent clauses, or between items in a series that already contain commas. A semicolon never goes before a dependent clause.

What is the difference between a colon and a dash on the SAT?

Both can introduce an explanation after a complete sentence. Dashes can also appear in pairs around a nonessential phrase, while colons cannot.

How many punctuation questions are on the Digital SAT?

Expect roughly six to eight boundaries questions per test, spread across both Reading and Writing modules. The exact number varies by form.