English grammar has many rules, and almost as many exceptions. Many times it is up to the author to dictate and choose different styles, but always for one reason: to communicate clearly. Take for instance the first sentence in this paragraph. Common grammar rules would dictate that there should not be a comma between the two parts of the sentence (because it’s not a list and it’s a comparison that should be equally represented on both sides of the word “and.” But, because I as a writer wanted to emphasize the second half of the sentence, I placed a comma before the word “and” which in effect gave the reader a literally “pause” before the main point was made.