Wikipedia:Commas exist for a reason

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WP:COMMAS

Punctuation is important, and the comma exists for a reason. Several reasons, actually. If someone has added or removed a comma in an article on your watchlist, do not simply reflexively revert the change, or edit war over it. Many commas are grammatically required, and many that aren't are stylistically preferred in formal writing. Furthermore, some low-register uses of commas are incorrect. Insertion or removal of a single comma can often totally change the meaning of a sentence, while in other cases having virtually no effect at all. When a comma-related dispute arises, do not simply assert that your preferred usage is the preferred one. First, see whether WP:Manual of Style/Punctuation covers the case in question and, if so, follow its advice. If not, consult multiple reliable sources on style, grammar, and usage to determine whether there is a generally accepted standard approach to that particular kind of case in formal writing, or multiple approaches. If a disagreement becomes intractable, see if there's a way to reword the sentence to obviate the issue entirely.

Patterns to look out for

"The meeting was attended by the CEOs of IBM, General Mills, and Procter and Gamble." The serial comma (which would normally be optional) is required in this case, because dropping it leaves an ambiguous mess, "... General Mills and Proctor and Gamble".
"Lil Bub ... may be the most recognizable cat on the Web. [...] She has an extra toe on each foot, giving her a total of 22 toes and a worldwide fan base of about 1.9 million, according to Facebook."[1] This is an absurdity, stating that her extra toes give her a fan base. There are several ways to rewrite this:
- "She has an extra toe on each foot, giving her a total of 22 toes. Lil Bub has a worldwide fan base of about 1.9 million" (the best option in this case)
- "She has an extra toe on each foot (giving her a total of 22 toes), and a worldwide fan base of about 1.9 million" (unconfused, but questionable writing, since the toes and the fan base are unrelated details)
- "She has an extra toe on each foot, giving her a total of 22 toes; and a worldwide fan base of about 1.9 million" (slightly jarring; a semicolon would usually only be used in a list of three or more items, but "She has" is followed only by two things)