It is nearly half past five, and we cannot reach town before dark. (来源：英语学习门户 http://www.EnglishCN.com)
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.
I had never been in the place before; so I had difficulty in finding my way about.
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:
As I had never been in the place before, I had difficulty in finding my way about.
If the clauses are very short, and are alike in form, a comma is usually permissible:
Man proposes, God disposes.
The gate swung apart, the bridge fell, the portcullis was drawn up.
6. Do not break sentences in two.
In other words, do not use periods for commas.
I met them on a Cunard liner several years ago. Coming home from Liverpool to New York.
He was an interesting talker. A man who had traveled all over the world, and lived in half a dozen countries.
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:
Again and again he called out. No reply.
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.
Walking slowly down the road, he saw a woman accompanied by two children.
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:
He saw a woman, accompanied by two children, walking slowly down the road.
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.
On arriving in Chicago, his friends met him at the station.
When he arrived (or, On his arrival) in Chicago, his friends met him at the station.
A soldier of proved valor, they entrusted him with the defence of the city.
A soldier of proved valor, he was entrusted with the defence of the city.
Young and inexperienced, the task seemed easy to me.
Young and inexperienced, I thought the task easy.
Without a friend to counsel him, the temptation proved irresistible.
Without a friend to counsel him, he found the temptation irresistible.
Sentences violating this rule are often ludicrous.
Being in a dilapidated condition, I was able to buy the house very cheap.
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:
A. Divide the word according to its formation:
know-ledge (not knowl-edge); Shake-speare (not Shakes-peare); de-scribe (not des-cribe); atmo-sphere (not atmos-phere);
B. Divide "on the vowel:"
edi-ble (not ed-ible); propo-sition; ordi-nary; espe-cial; reli-gious; oppo-nents; regu-lar; classi-fi-ca-tion (three divisions possible); deco-rative; presi-dent;
C. Divide between double letters, unless they come at the end of the simple form of the word:
Apen-nines; Cincin-nati; refer-ring; but tell-ing.
The treatment of consonants in combination is best shown from examples:
for-tune; pic-ture; presump-tuous; illus-tration; sub-stan-tial (either division); indus-try; instruc-tion; sug-ges-tion; incen-diary.
The student will do well to examine the syllable-division in a number of pages of any carefully printed book.
III. ELEMENTARY PRINCIPLES OF COMPOSITION
1. Make the paragraph the unit of composition: one paragraph to each topic.
If the subject on which you are writing is of slight extent, or if you intend to treat it very briefly, there may be no need of subdividing it into topics. Thus a brief description, a brief summary of a literary work, a brief account of a single incident, a narrative merely outlining an action, the setting forth of a single idea, any one of these is best written in a single paragraph. After the paragraph has been written, it should be examined to see whether subdivision will not improve it.