?Is a Comma Grammar

The Economist:

HAPPY National Grammar Day, everyone. Today’s offering is only marginally on grammar. We’ve asked “What is grammar anyway?” here at Johnson. The layperson would almost certainly answer “those difficult rules that are drilled into you in school about how to use the language.” The linguist would reply with nearly the opposite: grammar is made up of the rules of language that a competent native speaker uses almost without effort, by the definition of “competent native speaker”. You use grammar every time you construct a sentence, not just those times when you’re scratching your head about whether to use “who” or “whom”.
Here’s a good example of how laypeople and linguists differ on grammar: OnlineSchools.com has created this handy infographic on the much-discussed punctuation mark known as the Oxford comma.