This is from independent.co.uk (it showed up as a result on a website):

You have probably read The Girl with the Dragon Tattoo, or at least heard of it.

Or is a coordinating conjunction, so grammatically speaking, it should only be preceded by a comma if what follows is a independent clause.

However, in the example above:

or at least heard of it.

What follows is a dependent clause.

So why is there a comma before or?


Options are generally separated by commas.


You can have chicken, beef, or fish.

In your example there are two options: either you have read the book, or you have just heard of it.

You have probably read The Girl with the Dragon Tattoo, or at least heard of it.

The two options are correctly separated by a comma.

  • I thought you should only do this if there were three or more options. Like they mention in this SE question: english.stackexchange.com/questions/30516/…. "When a coordinating conjunction is used to connect three or more items or clauses ..."
    – alexchenco
    Sep 5 '19 at 10:35
  • 2
    @alexchenco in the question and answer you cite, there are loads of examples with just two options. It says that a comma is appropriate when the two clauses are independent. So you could say "You may have read the book or its sequel" because both are about reading. In your example, the two clauses are not dependent because one is about reading and the other is about hearing of it.
    – Astralbee
    Sep 5 '19 at 10:40
  • The answer says that a comma should be used to join two independent clauses. In my example, I have an independent clause and a dependent clause. The last one is a dependent clause because it doesn't have a subject.
    – alexchenco
    Sep 5 '19 at 10:47

Disclaimer: I'm not very sure about this, so correct me if I"m wrong.

I did a research and found this website. In it, they say:

The adverbs of concession set up contrast clauses [...] Use commas to introduce dependent clauses beginning with these words, even when the independent clause comes first.

Or at least isn't in the list of adverbs of concession. But I suspect or at least acts as contrast in my example.

Same with sentences that use let alone. As mentioned in this SE post:

[...] prefaced by "let alone" shows what a reasonable person might expect in contrast to the lesser option.

In short, another use of the comma is to show contrast.

Note: It could also be that the dependent clause is non-essential, like other poster mentioned. And therefore, it requires a comma.

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