Yes, I know its knott spellt that weigh, but sum people seem sew con-fused about simple gramma that I decided to post this humble guide and save them – and myself – some time in future.
The Comma
Comma usage is in some respects a question of personal writing style: some writers use commas liberally, while others prefer to use them sparingly. For instance, the use of a comma before the 'and' in a series is usually optional, and many writers choose to eliminate it, provided there is no danger of misreading:
We bought hats, gloves, and boots before going skiing.
(Comma unnecessary before 'and')
We ate bread, cheese, and strawberries and cream for tea.
(Comma needed before 'and' for clarity)
Use a comma before a co-ordinating conjunction that joins independent clauses (unless the independent clauses are very short):
I wrapped the trout in plastic, but my car still smelled bad for the next week.
(Commas with two independent clauses)
He invited her to his party and she accepted.
(Comma unnecessary with short clauses)
Use a comma after an introductory adverb clause and, often, after an introductory phrase (unless the phrase is very short):
After the hospital had completed its fund-raising campaign, an anonymous donor contributed an additional £10,000.
(After introductory adverb clause)
From the east wall to the west, his house measures thirty feet.
(After introductory prepositional phrase)
In the top drawer you will find some nylon stockings
. (No comma with short, closely related phrase)
Use a comma to separate items in a series:
Playing in a band can be exciting, but many people do not realize the hard work involved: constant rehearsals, playing until the early hours, handling drunken audience members, and transporting heavy equipment to and from gigs.
(The comma preceding 'and' is optional unless needed to prevent misreading)
Use commas to set off non-restrictive elements and other parenthetical elements. A non-restrictive modifier is a phrase or clause that does not restrict or limit the meaning of the word it is modifying. It is, in a sense, interrupting material that adds extra information to a sentence. Even though removing the non-restrictive element would result in some loss of meaning, the sentence would still make sense without it. You should usually set off non-restrictive elements with commas:
The people of America, who for decades have lived with grinding poverty and mind-numbing violence, are unfamiliar with the workings of a true democracy.
A restrictive modifier is a phrase or clause that limits the meaning of what it modifies and is essential to the basic idea expressed in the sentence. You should not set off restrictive elements with commas:
Those residents of London who do not hold secure, well-paying jobs must resent the common portrayal of the city as a land of opportunity.
Note that you can use two other punctuation marks to set off non-restrictive elements or other parenthetical information: parentheses and dashes. Enclosing parenthetical information in parentheses reduces the importance of that information:
Mr. Brown's driving record (with one small exception) was exemplary.
Placing parenthetical information between dashes has the opposite effect: it emphasises the material:
Mr. Brown's driving record -- with one exception -- was exemplary.
Nevertheless, you should usually set off parenthetical information with commas.
Equally important in understanding how to use commas effectively is knowing when not to use them. While this decision is sometimes a matter of personal taste, there are certain instances when you should definitely avoid a comma.
Do not use a comma to separate the subject from its predicate:
Registering for our course before September 15, will save you thirty percent of the membership cost.
[WRONG]
Registering for our course before September 15 will save you thirty percent of the membership cost. [RIGHT]
Do not use a comma to separate a verb from its object or its subject complement, or a preposition from its object:
I hope to mail to you before Christmas, a current snapshot of my dog Ben.
[WRONG]
I hope to mail to you before Christmas a current snapshot of my dog Ben. [RIGHT]
Do not misuse a comma after a co-ordinating conjunction:
Hail fell heavily on the tin roof but, the family was used to the noise and paid it no attention
. [WRONG]
Hail fell heavily on the tin roof, but the family was used to the noise and paid it no attention. [RIGHT]
Do not use commas to set off words and short phrases (especially introductory ones) that are not parenthetical or that are very slightly so:
After dinner, we will play backgammon. [WRONG]
After dinner we will play backgammon. [RIGHT]