Commas are used to separate introductory phrases from the main clause of a sentence. This helps clarify the structure and flow of the sentence.
Examples:
* After the meeting, we went out for lunch.
* In the end, she decided to stay.
* Despite the bad weather, we went for a walk.
However, some short introductory phrases can be omitted without causing confusion.
* Yesterday we went to the park. (Can be written as "We went to the park yesterday.")
* Right now I'm reading a book. (Can be written as "I'm reading a book right now.")
Here's a general rule of thumb:
* Use a comma after a short introductory phrase if it's longer than 3 words or if omitting the comma would create ambiguity.
* Omit the comma if the phrase is very short and the meaning is clear without it.
Ultimately, the best way to determine if a comma is needed is to read the sentence aloud and see if it sounds natural. If there is a pause before the main clause, a comma is probably needed.