6.2 Commas, Lists, and Conjunctions

The Serial Comma in Report Action Lists

Police reports are built almost entirely out of action sequences - an officer arrived, assessed the scene, spoke to witnesses, and made an arrest, often all in one sentence. Whenever a sentence lists three or more items or actions, each one needs to be separated by a comma, and the comma placed immediately before the final 'and' or 'or' - called the serial comma or Oxford comma - is the item that most often gets dropped under time pressure, and dropping it is exactly what creates ambiguity in a legal document.

Consider a report sentence naming three people who reviewed a case file: 'The file was reviewed by the sergeant, the lead detective and the officer's supervisor.' Without a comma before 'and,' a careful reader could momentarily misread 'the lead detective and the officer's supervisor' as one combined description rather than two separate individuals, because nothing visually signals where the second item ends and the third begins. Adding the serial comma removes that ambiguity entirely: 'The file was reviewed by the sergeant, the lead detective, and the officer's supervisor' now unmistakably names three distinct reviewers.

Note that a list of only two items joined by 'and' or 'or' never takes a comma at all - the comma-before-conjunction rule for lists applies starting at three items, not two. Consistently applying the serial comma across every action list in a report is a small habit that removes a recurring source of grouping ambiguity in exactly the kind of document where ambiguity has real consequences.

Coordinating Conjunctions: When the Comma Belongs, and When It Doesn't

The seven coordinating conjunctions - for, and, nor, but, or, yet, so, often remembered by the acronym FANBOYS - can join two independent clauses, two verbs sharing one subject, or two simple phrases, and the comma rule changes depending on which of those three jobs the conjunction is doing in a given sentence.

The fastest way to apply this rule correctly under time pressure is a one-question test: could the words following the conjunction stand on their own as a complete sentence, with their own subject? In 'The officer arrived at the scene, and the paramedics followed shortly after,' the words after 'and' - 'the paramedics followed shortly after' - form a complete sentence on their own, so the comma belongs. In 'The officer arrived at the scene and secured the perimeter,' the words after 'and' - 'secured the perimeter' - have no subject of their own; they simply continue describing what the one officer did, so no comma is used.

This distinction is a frequent source of choose-the-correct-sentence distractors, because inserting an unnecessary comma before a compound predicate (officer arrived, and secured) looks superficially similar to the correct comma-before-independent-clause pattern, but it is punctuating a single action sequence as if it were two separate statements.

Semicolons and 'However': Linking Two Related Statements Correctly

When a report needs to connect two closely related independent clauses using a conjunctive adverb - however, therefore, consequently, moreover - the required punctuation is a semicolon before the adverb and a comma after it, not a comma alone.

The second row above illustrates a comma splice - two independent clauses joined by nothing more than a comma, which is a punctuation error regardless of whether a conjunctive adverb like 'however' sits in the middle of it. A comma alone is never strong enough to join two full clauses on its own; it needs either a semicolon, a period, or a coordinating conjunction to do that job. Because 'however' frequently appears in report writing to flag a contrast - a witness who is confident about one detail but uncertain about another, an officer who observed one thing but not another - getting this pattern right shows up often enough to be worth memorizing as a fixed template: semicolon before, comma after.

That vs. Which: Restrictive and Nonrestrictive Clauses

The choice between 'that' and 'which' is not a matter of personal style - it signals whether the information that follows is essential to identifying what is being talked about, or merely additional detail that could be removed without changing which specific person or object the sentence means.

In the restrictive example, 'that was found on the suspect' is doing real identifying work - it tells the reader specifically which weapon is meant, presumably distinguishing it from other weapons mentioned elsewhere in the report. Remove that clause and the sentence becomes vague: 'The weapon was a folding knife' - which weapon? In the nonrestrictive example, 'which was found near the dumpster' adds a useful but non-essential detail; the sentence already knows exactly which weapon it means (there is apparently only one weapon under discussion), and removing the clause still leaves a complete, specific statement: 'The weapon was a folding knife.'

The removal test above is the fastest way to resolve this on the exam: delete the clause in question and ask whether the sentence still identifies the same specific thing. If deleting it leaves the reader unsure which item is meant, the clause is restrictive and must use 'that' with no surrounding commas. If deleting it leaves the sentence's core identification fully intact, the clause is nonrestrictive and must use 'which' set off by a comma on each side (or a single comma if the clause falls at the end of the sentence, as in the table example). Getting this backwards - putting commas around a restrictive 'that' clause, or leaving them off a nonrestrictive 'which' clause - is one of the more subtle distractor patterns on choose-the-correct-sentence items, because both versions of the sentence are grammatically legal English; only one of them says what the report actually needs it to say.