Which vs. that

Hello, Alan, Conchita and everybody.

Can you give me a hand with the following:

where should we use “that” and where “which” and in what cases these are interchangable?

e.g. This machine makes a very high-pitched noise WHICH birds and people cannot hear.

Why do we use “which” here and can “that” be substituted for “which”?

Thank you

Hi Galusya,

Very often you can change which for that. I have written some materials on relative pronouns (which/that/who/whose) and if you like you can have a look at them. You’ll find it here:
Relative Pronoun.

Please let me know if you find the material useful.


Precise writers maintain a distinction between that and which:that is used as a relative pronoun in restrictive clauses
and which in nonrestrictive clauses.

In the book that is on the table is mine,
the clauses “that is on the table” is used to distinguish one particular book ( the one on the table ) from another or others
( which may be anywhere,but not on the table)

In the book , which is on the table,is mine,
the which clause is merely descriptive or incidental.

The more formal the level of language ,the more important
it is to preserve the distinction between the two relative
pronouns ;but in informal or colloquial usage,the words are
often used interchangeably.

Professor Jan
I don’t understand that so and so.

Hi Alan,
Since I read your story I’ve been getting to understand when and how I should use these words properly.
(I’m still not a hundred percent sure though)
(It’s not your fault, unfortunately they cut out my brain and ate it)
What I’d like You to know is that I really liked this story of yours about your aunt.
Have you ever written novels?
If you have, I’d be happy to read them all,

Hi Spencer,

I’m delighted you liked my piece on relative pronouns and pleased that it helped a little. In answer to your question, I haven’t written any novels but I do enjoy writing and I have found over the years that writing about grammar inside an anecdote can help to explain parts of language that people find difficult to follow.

Best wishes