The Elements of Style/Rules

1. Form the possessive singular of nouns with 's.
Follow this rule whatever the final consonant. Thus write,

This is the usage of the United States Government Printing Office and of the Oxford University Press.

Exceptions are the possessives of ancient proper names in -es and -is, the possessive Jesus' , and such forms as for conscience' sake, for righteousness' sake. But such forms as Achilles' heel, Moses' laws, Isis' temple are commonly replaced by

The pronominal possessives hers, its, theirs, yours, and oneself have no apostrophe.

2. In a series of three or more terms with a single conjunction, use a comma after each term except the last.
Thus write,

This is also the usage of the Government Printing Office and of the Oxford University Press.

In the names of business firms the last comma is omitted, as

The abbreviation etc., even if only a single term comes before it, is always preceded by a comma.

3. Enclose parenthetic expressions between commas.
This rule is difficult to apply; it is frequently hard to decide whether a single word, such as however, or a brief phrase, is or is not parenthetic. If the interruption to the flow of the sentence is but slight, the writer may safely omit the commas. But whether the interruption be slight or considerable, he must never omit one comma and leave the other. Such punctuation as

or

is indefensible.

Non-restrictive relative clauses are, in accordance with this rule, set off by commas.

Similar clauses introduced by where and when are similarly punctuated.

In these sentences the clauses introduced by which, when, and where are non-restrictive; they do not limit the application of the words on which they depend, but add, parenthetically, statements supplementing those in the principal clauses. Each sentence is a combination of two statements which might have been made independently.

Restrictive relative clauses are not set off by commas.

In this sentence the relative clause restricts the application of the word candidate to a single person. Unlike those above, the sentence cannot be split into two independent statements.

The abbreviations etc. and jr. are always preceded by a comma, and except at the end of a sentence, followed by one.

Similar in principle to the enclosing of parenthetic expressions between commas is the setting off by commas of phrases or dependent clauses preceding or following the main clause of a sentence. The sentences quoted in this section and under Rules 4, 5, 6, 7, 16, and 18 should afford sufficient guidance.

If a parenthetic expression is preceded by a conjunction, place the first comma before the conjunction, not after it.

4. Place a comma before and or but introducing an independent clause.
Sentences of this type, isolated from their context, may seem to be in need of rewriting. As they make complete sense when the comma is reached, the second clause has the appearance of an after-thought. Further, and, is the least specific of connectives. Used between independent clauses, it indicates only that a relation exists between them without defining that relation. In the example above, the relation is that of cause and result. The two sentences might be rewritten:

Or the subordinate clauses might be replaced by phrases:

But a writer may err by making his sentences too uniformly compact and periodic, and an occasional loose sentence prevents the style from becoming too formal and gives the reader a certain relief. Consequently, loose sentences of the type first quoted are common in easy, unstudied writing. But a writer should be careful not to construct too many of his sentences after this pattern (see Rule 14).

Two-part sentences of which the second member is introduced by as (in the sense of because), for, or, nor, and while (in the sense of and at the same time) likewise require a comma before the conjunction.

If a dependent clause, or an introductory phrase requiring to be set off by a comma, precedes the second independent clause, no comma is needed after the conjunction.

For two-part sentences connected by an adverb, see the next section.

5. Do not join independent clauses by a comma.
If two or more clauses, grammatically complete and not joined by a conjunction, are to form a single compound sentence, the proper mark of punctuation is a semicolon.

It is of course equally correct to write the above as two sentences each, replacing the semicolons by periods.

If a conjunction is inserted, the proper mark is a comma (Rule 4).

Note that if the second clause is preceded by an adverb, such as accordingly, besides, so, then, therefore, or thus, and not by a conjunction, the semicolon is still required.

In general, however, it is best, in writing, to avoid using so in this manner; there is danger that the writer who uses it at all may use it too often. A simple correction, usually serviceable, is to omit the word so, and begin the first clause with as:

If the clauses are very short, and are alike in form, a comma is usually permissible:

6. Do not break sentences in two.
In other words, do not use periods for commas.

In both these examples, the first period should be replaced by a comma, and the following word begun with a small letter.

It is permissible to make an emphatic word or expression serve the purpose of a sentence and to punctuate it accordingly:

The writer must, however, be certain that the emphasis is warranted, and that he will not be suspected of a mere blunder in punctuation.

Rules 3, 4, 5, and 6 cover the most important principles in the punctuation of ordinary sentences; they should be so thoroughly mastered that their application becomes second nature.

7. A participial phrase at the beginning of a sentence must refer to the grammatical subject.
The word walking refers to the subject of the sentence, not to the woman. If the writer wishes to make it refer to the woman, he must recast the sentence:

Participial phrases preceded by a conjunction or by a preposition, nouns in apposition, adjectives, and adjective phrases come under the same rule if they begin the sentence.

Sentences violating this rule are often ludicrous.

8. Divide words at line-ends, in accordance with their formation and pronunciation.
If there is room at the end of a line for one or more syllables of a word, but not for the whole word, divide the word, unless this involves cutting off only a single letter, or cutting off only two letters of a long word. No hard and fast rule for all words can be laid down. The principles most frequently applicable are:

 Divide the word according to its formation:

Divide "on the vowel:"

Divide between double letters, unless they come at the end of the simple form of the word:



The treatment of consonants in combination is best shown from examples:

The student will do well to examine the syllable-division in a number of pages of any carefully printed book.