I was reading some material for work and felt the need to get some information about ‘that’ versus ‘which’, because of course good ol’ Microsoft Word told me the grammar was incorrect. Now, I have Fowler’s usage guide at home, but unfortunately I’m not at home. So I Googled “that which” and found Jack Lynch‘s site at Rutgers that explained everything (true, it’s American, but I believe it applies generally). I like learning.