In English, the rule is that you must separate words that aren’t part of the sentence but instead comment on the meaning of the sentence. Put another way, introductory words that appear at the beginning of a sentence are set off from what follows by commas. If you omit these words, the sentence still means the same thing. Common introductory words include yes, no, well, oh, and okay.
Read these examples twice, once with the introductory words and once without. See how the meaning stays the same?
Yes, you are allowed to chew gum balls during class, but don’t complain to me if you break a tooth.
No, you are not allowed to write the exam in blood as a protest against the amount of studying you need to do in order to pass this course.
Well, you may consider moving on to another topic if you have exhausted the creative possibilities of “My Favorite Lightbulb.”
Oh, I didn’t know that you needed your intestines today.
To sum up the rule on introductory words: Use commas to separate them from the rest of the sentence, or omit them entirely.
Which sentence is correct?
A. Well Ella plays the piano well when she is in the mood.
B. Well, Ella plays the piano, well, when she is in the mood.
C. Well, Ella plays the piano well when she is in the mood.
Answer: Sentence C is correct. If you omit the first word, the sentence means exactly the same thing. Well is an introductory word that a comma should separate from the rest of the sentence. In sentence A, there is no comma after well. In sentence B, the first comma is correct, but the second well shouldn’t be separated from the rest of the sentence because it’s not an introductory word.