which or that?

Source

From http://www.businesswritingblog.com/business_writing/2006/01/that_or_which.html

That usually introduces essential information in what is called a "restrictive clause." Which introduces extra information in a "nonrestrictive clause."

  1. Example from a recent email:

    • "I am offering a new class, Email Intelligence, that/which may be an excellent fit for your training needs and budget."

    • Does the clause (in red) introduce information that is essential to knowing which Email Intelligence class?

    • No. The clause provides extra information, so which is correct.

  2. Revised example:

    • "Among my new programs, I am offering a class that/which may be an excellent fit for your training needs and budget."

    • Does the clause (in red) introduce information that is essential to knowing which class?

    • Yes. The clause tells which class--a class that may be an excellent fit. Therefore, that is correct.