THE COMMA
495. The comma is the mark used to indicate a slight break in the thought.
There are a number of rules given for the use of commas. These rules, like the rules for the use of capitals, you cannot commit to memory; but, after repeated practice in your own writing and paying attention to your reading, you will gradually develop an instinctive sense of the use of the comma. Select some book which you are reading and go through it, noticing especially the use of the commas. See if you can determine the reason which prompted the author to place his commas where he did. Notice, also, what effect the placing or the omission of the comma would have upon the meaning of the sentence.
496. The Comma indicates the slightest degree of separation between the parts of a sentence.
RULE 1.
497. Words, phrases and clauses, forming a series and used in the same construction, should be separated from each other by commas when the conjunctions are omitted.