Grammar – Comma Before ‘That’ When It Refers to Something That Doesn’t Immediately Precede It

The meaning is the same either way. However, when writing sentences - especially when writing something formal such as an essay - one should use commas after their transition word or phrase that starts a new sentence.

For example, notice how I started this sentence with my transition phrase "for example" and put a comma after it? Of course, commas are useful for starting sentences out, as well as breaking up the thoughts in a single sentence.

I italicized the transition words/phrases above. Here is a site with phrases if you want to know how to add variety to your words. It's divided into different categories.

I think the "rule" is really more of a guideline to help you organize your thoughts around the use of commas. Which is all commas really are -- a way to organize the written word by adding significant pauses to separate parts of a sentence. In practice, some people use commas far less than they should. Other people like to string together sentences with commas until they're the proverbial Mark Twain Literary German.

So a comma is a pause in the conversation. It's not necessary to use commas, but it can be convenient to your readers to help them follow the flow of your thoughts.

To return to your guideline, it seems like the videos recommend using a comma in situations where you're going to change the direction of the action. "I started the car and drove away," is no surprise. That's what cars do. But, "I started the car, and the engine caught on fire," does not flow smoothly from one action to the other. The comma helps define that you, the writer, did not expect the second action to happen. If you were to say this to another person you'd probably insert a pause before the "and" just to add some drama to your anecdote.

So imagine a conversation, and insert commas where they feel appropriate. The more familiar you get with where English speakers insert pauses, the more natural it will become.