what is the difference between which and that

- We tend to think that 'which' and 'that' are interchangeable.
- But, there is a subtle difference.
- The easiest way to remember is: 'that defines, which describes'.
- 'That' gives an essential part and 'which' gives an optional part.
- 'That' indicates a specific person, object, etc. 'Which' adds optional information.
- These are restrictive and non-restrictive clauses in technical terms.
- For example: I like the painting that you made.
The painting, which I like, has been sold for two lakh rupees.