See what you can infer from this sentence: When my three siblings and I entered the dark house, my brother, Marky, got scared. A careful reader would know instantly that the author had one brother and two sisters.

Why? Because of the commas surrounding Marky, which tell us that the brother’s name is nonessential. The commas enable the writer to say my only brother, whose name is Marky in three words.

Suppose the writer had entered the house with three brothers. In that case, my brother got scared would not tell us enough. With more than one brother involved, the sentence would have to say my brother Marky got scared—no commas. The absence of commas makes the brother’s name an essential element, and it is essential because without Marky we wouldn’t know which brother the writer meant.

Along the same lines: Mark Twain published his beloved book, “The Adventures of Tom Sawyer,” in 1876. The commas must go; the book’s title is essential. It is undeniable that Twain wrote more than one beloved book. Without commas the sentence would say what it means: that Twain wrote many beloved books, and Tom Sawyer is one of them. If the book’s title were nonessential, then Mark Twain published his beloved book in 1876 would not be such an inadequate sentence.

Here’s a comma gaffe many inexperienced writers make: The film features the world-famous actor, Robert DeNiro. Delete the comma fencing off Robert DeNiro. It mistakenly tells the reader that the actor’s name is nonessential—but the sentence makes little sense without DeNiro’s name in it.

The terms wife and husband always require commas in sentences like this: My wife, Marie, enjoyed meeting your husband, Lucas. This is because we can have only one spouse at a time, so their first names are nonessential, supplementary information.

Note: The following sentence is an exception to the wife-husband rule above: Cuthbert Simms and wife Marie sailed to the Bahamas last weekend. No comma is called for because in that sentence wife is not a noun, but rather an adjective modifying Marie.

The rule for grandmother and grandfather is the opposite of the wife-husband rule. This sentence is correct without commas: My grandmother Bess thinks your grandfather Horace is a twit. Everyone has two biological grandmothers and two biological grandfathers, so the names Bess and Horace are essential information.

Punctuation proficiency is crucial to serious writing. Don’t take the humble little comma for granted.