+1
I'm preparing a lesson on non-defining relative clauses to give a comment (explanation / consequnce) on the main clause of a sentence. In some cases it seems to be correct to use either which is why* or *which means to start the relative clause:

My dog has long hair, which means she needs grooming regularly.
which is why

But in other cases only which is why seems to be correct:

I have locked my keys in my car, which is why you saw me breaking the window.

I've tested many sentences (what sounds right to me, as a native english speaker), but have failed to find a rule, yet feel that there should be one.  Can anyone help?

Thank you!
+1
which means (that) ... ~ which has as a consequence (that) ...

That the dog needs grooming regularly is a consequence of the fact that the dog has long hair.

On the other hand, that you saw me breaking the window is not a consequence of the fact that I locked my keys in the car, so which means (that) won't work.

But you can have:

I locked my keys in the car, which means I had to break the window.

Here, my having to break the window is a consequence of the fact that I locked my keys in the car.
_______________

which is why is more ambiguous. It can refer to a consequence (like which means does) or to a more general explanation of the association of circumstances.

I locked my keys in the car, which is why you saw me breaking the window.
I locked my keys in the car. This explains the fact that you saw me breaking the window.

CJ
Comments  
Hi,
Richard from PiraIn some cases it seems to be correct to use either which is why* or *which means to start the relative clause.
The phrases in question have different meanings:

Which is why -- for this reason; therefore; hence.

Which means -- that is; namely; in other words.

Take your sentence as an example:

I'd locked my keys in my car, which is why / which means you saw me breaking the window.

Let's see if the following sentence still makes sense:

I'd locked my keys in my car; therefore (which is why), you saw me breaking the law.

Now let's move on to this sentence:

I'd locked my keys in my car, that is (which means), you saw me breaking the law. X

Just use other words to check if your sentence is still meaningful and reasonable.

If both work for you, choose the one that fits your intended meaning better.

Regards
Students: Are you brave enough to let our tutors analyse your pronunciation?
 CalifJim's reply was promoted to an answer.
Regards (sorry I could not find your name) and CalifJim. Many thanks for your quick replies. I found Jim's pointer to testing consequence beyond association of circumstances invaluable!

Richard.

This has been answered in detail here: https://www.englishforums.com/blog/which-means-how-to-use-it/

Teachers: We supply a list of EFL job vacancies