8.2 Boundaries: Punctuation That Joins Clauses

Section 8.1 taught you to diagnose a fragment, run-on, or comma splice. This section inventories the legal joints. On PSAT 8/9 Boundaries items, the four choices often look almost identical except for a period, semicolon, colon, dash, or comma. The stem is still Which choice completes the text so that it conforms to the conventions of Standard English? The credited response is the punctuation that matches the clause types on either side of the blank.

This independent OpenExamPrep lesson helps 8th and 9th graders study clause punctuation for the PSAT 8/9. OpenExamPrep is not a College Board partner and does not claim official approval, review, partnership, or exact equivalence with College Board materials.

College Board's Student Question Bank note is practical: Boundaries choices contain different punctuation. If the four options swap words rather than marks, you have probably moved into 8.3 Form, Structure, and Sense: Verbs and Agreement or 8.4. Still start with the clause test. Punctuation rules are meaningless until you know whether each side can stand alone.

The toolkit for two independent clauses

When both sides of the blank are independent, you may use one of these joints:

A period is always legal between independents. Choose a semicolon when the second clause is tightly related, not a new topic. Choose FANBOYS when you want an explicit relationship (but contrast, so result, and addition). Choose a colon when the first clause announces something the second clause specifies. Choose a dash when the second thought interrupts or explains with extra punch. Do not pick a dash or colon just because it looks advanced. If the second clause does not explain or specify the first, a colon is the wrong tool.

FANBOYS is the seven coordinators: for, and, nor, but, or, yet, so. The comma sits before the coordinator, not after it. The team finished the prototype, but it still needed an update is legal. The team finished the prototype but, it still needed an update is not. A semicolon plus FANBOYS is a common trap: The team finished the prototype; but it still needed an update stacks two joining systems. Use the comma with FANBOYS, or drop but and keep the semicolon.

Introductory dependent clauses take a comma

When the dependent clause comes first, Standard English uses a comma before the independent clause:

When the bus reached the field station, the students unloaded the crates.

When the independent clause comes first and the dependent clause is essential to the meaning, you usually skip that comma:

The students unloaded the crates when the bus reached the field station.

That pattern is not a comma splice. The second group cannot stand as a sentence, so a comma-plus-nothing would be the wrong worry. The splice danger appears only when both sides are independent.

Conjunctive adverbs are not FANBOYS

Words such as however, therefore, moreover, nevertheless, consequently, meanwhile, instead, otherwise, furthermore, and accordingly show a logical turn, but they are not coordinators. They cannot sit after a comma between two independents:

The upper trail was icy, therefore the ranger closed the loop.

That sentence is a comma splice wearing a serious vocabulary word. Legal versions:

• Period: The upper trail was icy. Therefore, the ranger closed the loop.
• Semicolon: The upper trail was icy; therefore, the ranger closed the loop.

Notice the semicolon (or period) before therefore and the comma after it when the adverb opens the second clause. A comma on both sides of therefore while a comma also joins the clauses (icy, therefore, the ranger) is still a splice.

This is the exact place students mix up Boundaries with Transitions. A Transitions item might ask whether however or therefore is the better relationship. A Boundaries item assumes the relationship word and asks whether the marks around it are legal. Getting the logic right does not save an illegal comma.

Colons: the second clause explains the first

A colon between clauses is legal when the first clause is independent and the second clause explains, illustrates, or specifies what the first just announced:

The lab rule was simple: no food could sit on the same counter as the water samples.

The lab rule was simple can stand alone. The second clause tells you what the rule was. That is the job of this colon.

Do not use a colon after a verb or preposition that is still waiting for its object: The kit included: notebooks, folders, and pens is the wrong pattern for this test. Keep The kit included notebooks, folders, and pens or recast: The kit included three tools: notebooks, folders, and pens.

If the second group is not an explanation of the first, use a period or semicolon instead. The lab opened at seven: the bus was late does not make the second clause a specification of the first. Those are two loosely related events, not a label-plus-definition.

Dashes: extra punch, same extra-info job

A single dash can do colon-like work for an abrupt explanation:

The cooler failed at noon—every sample had to be recollected.

A pair of dashes can wrap extra information the way a comma pair does:

The field station—the only building with electricity—had no refrigerator.

Rules at grade 8–9:

• Do not mix a dash on one side of an extra phrase with a comma on the other.
• If you open extra information with a dash, close it with a dash (or end the sentence).
• Do not use a dash as a mood decoration in the middle of a legal comma + FANBOYS joint.

If two choices both look legal—one colon, one dash—reread whether the second thought is an explanation of the first (colon or dash) or simply a related independent (period or semicolon). On many items only one mark is offered in a grammatical option.

Essential versus nonessential information

Essential (restrictive) information tells you which person or thing you mean. It takes no commas:

The students who finished the quiz early started the greenhouse lab.

Without who finished the quiz early, you would not know which students. The clause is needed, so it is not wrapped in commas.

Nonessential (extra) information can be deleted and you still know which noun you mean. It takes a comma pair (or dash pair):

The eighth-grade science class, which meets in Room 12, started the greenhouse lab.

There is one eighth-grade science class in the sentence's world. Which meets in Room 12 is extra location. Both commas are required. A comma only before the clause, with none after, leaves the extra information unclosed.

A practical delete test: cross out the extra group. If the sentence still names the same people clearly, you needed commas. If the meaning jumps from "some of them" to "all of them," the clause was essential and should stay comma-free.

Relative-word habit at this grade band: that usually introduces essential information (no commas). Which often introduces extra information (commas). Who can do either, depending on whether you need the clause to identify the person.

Lists

A simple list of three or more items uses commas between items, including before and:

The kit included notebooks, folders, and pens.

That serial comma keeps folders and pens from gluing into one blob. Do not put a comma between the subject and the verb: The kit, included notebooks is illegal.

When the list items themselves contain commas, step up to semicolons between items:

The tour stopped in Portland, Oregon; Boise, Idaho; and Reno, Nevada.

Without those semicolons, the city-state commas collide and the list becomes unreadable. That is still a Boundaries job: choosing the mark that shows where one unit ends.

Two-item lists joined by and or or do not take a comma: notebooks and pens, not notebooks, and pens, unless you have two full independent clauses (back to FANBOYS).

Worked item: conjunctive adverb

The upper trail was icy _______ therefore, the ranger closed the loop above the waterfall.

Both sides are independent. Therefore is not FANBOYS. The legal joint is a semicolon (or a period) before therefore. A comma before therefore is a splice. No mark is a run-on. A second semicolon after therefore chops the adverb off from its clause.

Worked item: extra information

The eighth-grade science class _______ started the greenhouse lab without waiting for the bell.

If the blank is which meets in Room 12 as extra identification of a single class, you need , which meets in Room 12, with both commas. A semicolon before which would demand an independent clause on the second side and fails.

How this looks in a module

Conventions items are grouped and then ordered easiest to hardest, independent of which punctuation mark is in play. An early item may be comma + but versus a splice. A later item may mix a colon with a nonessential dash pair. Spend your extra seconds on the last item in the cluster. You still cannot return after the 32-minute module locks. Module shape is in 5.1 How the Reading and Writing Section Is Built.

Quick checks

• Two independents: period, semicolon, comma + FANBOYS, or colon/dash only if the second explains the first.
• However / therefore between clauses: semicolon or period, never a comma alone.
• Extra info: comma or dash pairs; needed info: no commas.
• Lists: commas between simple items; semicolons when items already contain commas.
• Do not put a semicolon before FANBOYS, and do not put a comma between a subject and its verb.

/practice/psat-89Practice questions with detailed explanations