Punctuation Rules: English Sentence Basics

Punctuation is used to signify stops and pauses in the written word to convey emotion, conviction and sentence rhythm. There are several different symbols used in writing English. External punctuation signifies an end of a complete sentence, or thought. The symbols discussed here are: a period, a question mark or an exclamation point. Internal punctuation marks within a sentence are the comma, the semicolon, the colon and quotation marks. They help the reader pause, read lists, and sort out dependent or independent thoughts.

Periods and sentences (.)

Sentence that ends with a period, indicates that what came before the symbol is either a statement or a command. Example: The cat took a nap.

Periods are also used in lists after numbers, and to indicate something is missing from the text (Example: ...)

Question marks and sentences (?)

Seeing a question mark at the end of a sentence means that the information contained within is a question and the person asking the question expects an answer. Example: When will your homework be done?

Exclamation point at the end of a sentence (!)

Seeing an exclamation point at the end of a sentence indicates strong feeling, such as fear or excitement. Example: Congratulations! It's so great to see you again! Be careful using the exclamation point too much. Frequent use of an exclamation point diminishes the intent and makes writing sound fake and overly emotional.

Commas within a sentence (,)

Commas are symbols or punctuation marks that are used for two purposes. The first purpose is to offset a part of the sentence that might get jumbled up to the reader if it isn't set apart. Example: Jack, the tailor, noticed that John was growing by the fact that his socks were showing beneath his pants hem.

The second time a comma is used is when it is used to separate different things such as "cats, dogs, and hamsters" in a list or string of words. When commas are used, the reader will pause slightly to take a breath.

Semicolon within a sentence (;)

Semicolons are used to join two independent clauses or thoughts when a coordinating conjunction (and, but, or, or nor) is omitted. The second clause could be read as a separate sentence, but writers' use a semicolon to keep the reader reading. Example: Janet is trying out for soccer; Joan is already on the team.

Use a semicolon when there are multiple commas in a sentence to help reading, or when you want to make a stronger point. Example: I graded Tom's, Dick's, and Harry's papers; Janet, Joan's and Jack's were missing.

Colon within a sentence (:)

Colons are used between independent clauses when the second explains the first, or with lists. Examples: I have to graduate with an A: I need to do my homework and pass my tests. Or "We are going to mix the following ingredients: peppers, mushrooms and onions."

Quotation marks ("")

Quotation marks are used to show what someone said. Example: Mark said, "Take off your shoes." They are also used to set off "special words" or to refer to a title, "The Cat in the Hat" book. Periods and commas always go inside the quotation marks but question marks and exclamation points only go inside when it applies directly to the information being quoted. It goes outside the quotation marks if the punctuation applies to the entire sentence.

Source
"The Gregg Reference Manual" UOP Custom Edition