The Elements of Style, Fourth Edition

The number of the subject determines the number of the verb.

Exceptions are the possessives of ancient proper names ending in -es and -is,

Restrictive clauses, by contrast, are not parenthetic and are not set off by commas.

do not use periods for commas.

Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the

When the main clause of a sentence is preceded by a phrase or a subordinate clause, use a comma to set off these elements.

In these sentences, the clauses introduced by which when, and where are nonrestrictive; they do not limit or define, they merely add something.

Place a comma before a conjunction introducing an independent clause.

Use a colon after an independent clause to introduce a list of particulars, an appositive, an amplification, or an illustrative quotation.

A dash is a mark of separation stronger than a comma, less formal than a colon, and more relaxed than parentheses.