🗽 Comma or no comma with relative clauses 🗽

Boring, I know. But important.

Stop explaining the need for commas, or the lack thereof, with relative clauses with the help of "essential vs. non-essential information." This is not helpful. "Defining vs. non-defining" is probably more helpful. But, obviously, I have the most helpful explanation.

Everything hinges on whether there is one of something or more than one of something.

1️⃣ "My brother, who lives in New York, has three cats." I have one brother.
2️⃣ "My brother who lives in New York has three cats." I have more than one brother. One lives in New York. Another one(s) lives elsewhere.

3️⃣ "The entrance, which is located on the southern side, has been renovated." The place has one entrance.
4️⃣ "The entrance which is located on the southern side has been renovated." The place has more than one entrance. The entrance on the southern side has been renovated. The one located elsewhere hasn't.

So the meaning hinges on the comma, and the absence of the comma can create sentences that don't make sense. For example, "It reached 50,000 which was the highest recorded level." This sentence means there are more than one 50,000 marks: one was the highest level and one (or more than one) wasn't, which doesn't make sense.

More creative and context dependent uses:

5️⃣ Me talking to my students: "St Petersburg, where I live, is a gloomy place." I am Russian. Most of my students are Russian. I assume we all understand there is only one St Petersburg.

6️⃣ But I often badmouth St Petersburg because of its bad weather. So a student might get indignant and exclaim, "Well, the St Petersburg where I live is a nice, vibrant place." The meaning here is that, metaphorically speaking, there are two St Petersburgs, i.e. two perceptions of the city.

7️⃣ When I go to Florida, I might meet someone who lives in St Petersburg in this state. They might tell me, "St Petersburg is a cute little town." I might reply, "The St Petersburg where I live is neither cute nor little." There are two St Petersburgs, literally.

To sum up, what makes the information essential or non-essential and the clause defining or non-defining is whether there is only one or more than one of something.

Did this post make your head spin? This is not even an exhaustive explanation...