lll. The Main Punctuation Marks
1. The Full Stop [.]
a. This is the strongest punctuation mark, making the most definite pause (in reading aloud or silently) when used at the end of a sentence. As shown in the previous examples, it is used at the end of sentences unless they are questions, strong exclamations or strong commands. It is also called a period and a full point.
b. It is used to indicate omitted letters in abbreviations, such as Mon. for Monday or a.m. for ante meridiem (Latin for 'before noon'), and in initials, as in B.K. Smith. Common abbreviations, and those of scientific terms and names of organisations, are now frequently spelled without full stops, e.g. Mr (Mister), Dr (Doctor),DNA (deoxyribonucleic acid), cm (centimetre), UK (United Kingdom). A distinction is sometimes made between a contraction, where the last letter of the contracted form is the last letter of the original word, needing no full stop (e.g., Dr for Doctor) and an abbreviation in which its last letter is not the last letter of the full word, needing a full stop (e.g., Prof. for Professor). If an abbreviation which takes a full stop, such as etc. (et cetera, Latin for 'and so forth'), comes at the end of a sentence, there is no need for another full stop to end the sentence: I will send you the members' names, addresses, etc.
c. Full stops are often used in amounts of money: £10.20 and in times: 3.20 a.m. When used in numbers as a decimal point, it is usually just typed as a full stop, but this stop should strictly be raised above the line [·], as in 9·66. On most computers, this can be obtained by having Num Lock on, holding Alt and typing 0183.
d. Three full stops together (the Ellipsis or suspension dots) [. . .] are used to show an unfinished sentence, omission of part of a sentence: The letters of the alphabet are a, b, c, ... x, y, z, or hesitation in speech: She would invite him to. . . No, that was unthinkable.
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2. The Question Mark [?]
This is used to end a direct question where an answer is normally expected: "Where do I buy a season ticket?" It is not used for an indirect question (which reports a direct question), to which no answer is expected: She asked where she could buy a season ticket. It is used at the end of rhetorical questions(*) even though no answer is expected. A question mark is needed when question phrases (question tags) are added to statements: "The concert is tonight, isn't it?"
3. The Exclamation Mark [!]
This is used after exclamations showing a high degree of surprise: "Fancy meeting you here!" or strong emotion: "You filthy cheat!" or special emphasis: "You are so beautiful!" or an expletive(**) "Damn!" It is also used after strong commands or requests, especially where the voice would be raised in speech: "Don't shoot!" Mild requests or commands usually end with a full stop: "Come here, please." Using too many exclamation marks weakens their impact.
(*) A question, often implicitly assuming a preferred (usually negative) answer, asked so as to produce an effect rather than to gain information.
(**) An oath or swear word.
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4. The Comma [,]
A comma has many uses, including:
a. To separate items in a list:
Jake stole her purse, keys, cheque book and credit cards. There is no need for a comma before the 'and' unless the sense demands it. The comma before the final 'and' is helpful in: The children played cops and robbers, hide and seek, and hopscotch. Some people, especially in the USA, use commas before 'and' even in simple lists as in the Jake stole... example above. Commas can also be used to separate a series of phrases or clauses.
