3.1 Commas: Essential Rules

Why Commas Matter on the TEAS

Commas are among the highest-yield punctuation marks on the ATI TEAS 7 English and Language Usage section. Conventions of standard English include correct comma placement in lists, compound sentences, introductory elements, and clause boundaries. A single misplaced or missing comma can change meaning—especially dangerous in healthcare charting, where "Patient refused medication, nurse notified provider" reads differently from a run-on or a comma splice that blurs who did what.

This section covers the essential comma rules TEAS writers expect you to apply under time pressure. You will see how each rule works in ordinary academic sentences and in realistic nursing and allied-health notes. Later chapters return to comma splices as a full sentence-structure error; here you get a preview so you can already reject illegal comma-only joins between complete sentences.

Series and Lists (Including the Serial Comma)

When three or more words, phrases, or clauses appear in a series, separate the items with commas. Most academic and healthcare style guides prefer the serial comma (also called the Oxford comma)—the comma before the final and or or.

TEAS trap — missing serial comma clarity: Items often present two otherwise similar sentences and ask which is clearer or correct. Prefer the version that uses the serial comma when omitting it could make the last two items look like a single appositive rename of the first.

Healthcare charting example: "Report weight, blood pressure, and oxygen saturation every four hours" is clearer than a list that collapses the final pair. Parallel structure in the list items also helps scorers (and later, your own notes) stay readable.

Compound Sentences and Coordinating Conjunctions

An independent clause can stand alone as a complete sentence: it has a subject and a predicate and expresses a complete thought. When you join two independent clauses with a coordinating conjunction, place a comma before the conjunction.

Memorize the coordinating conjunctions with the mnemonic FANBOYS:

Correct compound pattern: Independent clause + comma + FANBOYS + independent clause.

• The patient reported dizziness, and the nurse rechecked orthostatic vitals.
• Pain decreased after medication, but the patient still could not ambulate without assistance.

Do not use this comma when the second part is not an independent clause:

• The nurse documented the wound and changed the dressing. (Compound predicate; same subject; no comma needed before and.)

Comma Splice Preview (High-Yield Error)

A comma splice joins two independent clauses with only a comma and no coordinating conjunction:

• Incorrect: The IV site looked swollen, the nurse stopped the infusion.
• Fix with FANBOYS: The IV site looked swollen, so the nurse stopped the infusion.
• Fix with semicolon: The IV site looked swollen; the nurse stopped the infusion.
• Fix by splitting: The IV site looked swollen. The nurse stopped the infusion.

TEAS stem language may ask you to identify the sentence that is punctuated correctly or to choose the best revision. If you see two full sentences glued by a lone comma, treat that option as wrong unless a FANBOYS word follows the comma.

Introductory Elements

Place a comma after material that comes before the main clause and sets the stage: single words, transitional phrases, prepositional phrases of some length, participial phrases, and dependent (subordinate) clauses.

Short openers sometimes appear without commas in informal writing, but TEAS-style academic English generally keeps the comma after a clear introductory clause or multi-word phrase. When the introductory element is a full dependent clause beginning with words such as because, although, when, if, since, or while, the following comma is expected.

Healthcare charting example: "When the patient's temperature reached 39°C, the nurse notified the provider and initiated the fever protocol." The dependent clause opens the sentence; the comma marks the boundary before the independent clause that states the actions taken.

Essential vs. Nonessential Clauses and Phrases

This distinction is a classic TEAS (and ACT/SAT-style) trap.

• Essential (restrictive) information is needed to identify which person or thing you mean. Do not set it off with commas.
• Nonessential (nonrestrictive) information adds extra detail about an already identified noun. Set it off with commas on both sides (or a single comma if it ends the sentence).

Restrictive "That" vs. Nonrestrictive "Which"

In careful American academic usage tested on TEAS-style items:

• Use that (typically without commas) to introduce essential clauses: The protocol that the unit adopted reduced falls.
• Use which (typically with commas) to introduce nonessential clauses: The fall-prevention protocol, which the unit adopted last month, reduced falls.

If removing the clause would leave you unsure which protocol, patient, or medication is meant, the clause is essential—no commas, and often that. If the noun is already clear (a proper name, the specific one already identified), the clause is extra—commas, and often which.

Appositives follow the same logic. Essential appositives identify; nonessential appositives rename with commas:

• Essential: My colleague Nurse Patel floated to the ICU. (Which colleague?)
• Nonessential: Nurse Patel, a float pool RN, covered the ICU. (Already named.)

Dates, Addresses, and Related Comma Uses

Coordinate adjectives (adjectives that independently modify a noun and could be joined by and) also take commas: a calm, cooperative patient. Do not insert commas between adjectives in fixed cumulative order: a small plastic syringe (not "small, plastic" as if both were freely rearrangeable descriptors of equal rank).

Quick Decision Flow for TEAS Items

1. Are you looking at a list of three or more? Use commas between items; prefer the serial comma for clarity.
2. Are two independent clauses joined by FANBOYS? Comma before the conjunction. Comma alone = splice (wrong).
3. Does something open the sentence before the main clause? Usually add a trailing comma after the intro.
4. Is the clause or phrase required to identify the noun? No commas. Extra info? Commas.
5. Dates and city–state pairs in running text usually need the standard separating commas.

Apply these five checks and most TEAS comma questions become mechanical rather than "by ear." Ear training still helps for reading, but the exam rewards rule-based choices when two options both "sound fine."