Any comma essentially represents a pause – one that gives your readers the signal to take a quick breath before continuing with the next portion of the sentence. When a comma is used, it places more emphasis on what immediately precedes and follows the comma. Sometimes, there is no grammatical rule that dictates the use of a comma in a particular spot within a sentence, but the use of one, creating a pause, can create an emphasis that does not exist without the comma. Consider the following examples:
Example 1: Yesterday, I experienced the worst day of my life.
Example 2: The novice guitarist was butchering my favorite song, quite badly.
In both examples, the comma is grammatically unnecessary. It does, however, create a pause that places more emphasis. In the first example, the emphasis of the sentence shifts from “worst day of my life” to “yesterday” and “I.” In the second example, the emphasis is placed on “butchering my favorite song” and “quite badly.” You might do this to emphasize the extent to which the song is butchered.
It is important to consider the overall meaning you are trying to convey with a sentence when adding a comma as a pause to emphasize something, as putting a comma in the wrong spot can alter the meaning of your sentence.
Sometimes sentences require your readers to shift gears in a sense. You might make a statement and look for confirmation by turning the sentence into a question. Similarly, a comma represents the shift from one thing to another.
Example 1: You plan on watching the Super Bowl, right?
Example 2: Sometimes you might feel a little nervous in new environments, even when you are a little excited at the same time.
Both examples above represent a shift in the sentence. Using the comma clues your readers that the shift is about to occur, even when they are not consciously aware of the shift happening.
Normally coordinate elements do not require the use of a comma, as they are connecting similar items, thoughts or phrases. However, when the elements are contrasting, a comma is necessary to notate the contrast. See the below examples:
Example 1: She was happy most of the day, but sad by the end of it.
Example 2: She received a high mark on the exam, not the low one she expected.
Example 3: Her dancing partner was graceful, yet clumsy with certain steps.
In each of the examples above, the part of the sentence that comes after the comma contrasts the part that comes before it. Yet, both parts are essential to convey the intended meaning.