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Is using a comma then an "and" or an "or" after it proper punctuation? Example:

  • I fell over, and hurt my knee.
  • Should I go, or not?
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Whether it is correct to use a comma before a coordinating conjunction ("and", "but", "or", "nor", "for", "yet", "so") depends on the situation. There are three primary uses of conjunctions:

  1. When a coordinating conjunction is used to connect two independent clauses, a comma is always used. Examples:

    • I hit my brother with a stick, and he cried.
    • The rain stopped, and the sun came out again.
    • Should I eat dinner, or should I play a game?
  2. When a coordinating conjunction is used to connect a dependent clause, a comma is never used. This includes both of your given examples. Other examples:

    • The boy ran to his room and cried.
    • Frank is a healthy and active child.
    • Should I eat dinner or play a game?
  3. When a coordinating conjunction is used to connect three or more items or clauses, a comma is optional (though I personally prefer to use one). Examples:

    • I bought cheese, crackers, and drinks at the store.
    • Should I eat dinner, play a game, or go to the store?
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    See also the Oxford/Serial comma debate (your point 3): Serial comma. – user9853 Jun 20 '11 at 2:33
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    I agree with your examples, but I think the labels on 1 and 2 could be improved. The first group is about independent clauses, not main clauses. The second one is about non-independent or dependent clauses, not subordinate clauses (they are dependent because they are elliptical). – Cerberus_Reinstate_Monica Jun 20 '11 at 3:49
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    @rintaun: I agree with the main points of your answer but disagree with using always and never. Between very short and closely connected independent clauses, the comma can be omitted. ("He played the guitar and she sang.") In compound predicates, a comma is not usually used, though it may be needed to avoid confusion or indicate a pause. ("She recognized the man who entered the room, and gasped" vs. "She recognized the man who entered the room and gasped.") CMOS 6.32, 6.34 (15th ed.) It would be better to use the word usually. – Tragicomic Jun 22 '11 at 11:41
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    Also, in your second point, "cried" is not a dependent clause. It cannot be a dependent clause because it does not have a subject. It is just part of a compound predicate. Here is an example of a sentence with one independent and once dependent clause: "The boy ran to his room because he was crying." – Tragicomic Jun 22 '11 at 11:42
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    People who didn't/don't spend time thinking about English grammar tend to think of comma usage as an arbitrary rule that just needs to be memorized, but as @KaiNoack pointed out, it's about resolving ambiguity. If you're writing a sentence and are unsure about comma omission (or addition), consider the possible ways in which your sentence can be interpreted, and try to remove any ambiguity which can leave your reader misunderstanding your point... which is, after all, the point. – squidbe Oct 14 at 18:14
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Getting comma usage with and and or can be tricky sometimes, and even the best of us will mess it up once in a while.

Here's a good guide: http://www.grammarbook.com/punctuation/commas.asp

And some examples:

  • I fell over and hurt my knee.
  • I fell over, hurt my knee , and got stitches.
  • I like the colors red and blue.
  • I like the colors red, blue , and purple.
  • You can buy an apple, a pear , or an orange.
  • I can go or stay - which would you prefer?

When used in a list, and and or never take a comma when the list has two items; when it has more, it is generally a good idea to use the comma.

When used as a conjunction it is generally a good idea to use the comma (unless the phrases are very short).

4

"I went to Japan and returned in 2009" is correct but rather unspecific. It could imply either "I went [say, in 2003] and returned in 2009" or "I went and returned in 2009". The comma in "I went to Japan, and returned in 2009" points to the former; With two commas, "I went to Japan, and returned, in 2009" definitely implies the latter.

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