pronouns - "that which" used together

When I read essays from Eliot, I find him using "that which" frequently, e.g.

1. the combination which is the murder of Agamemnon is probably as complex as that which is the voyage of Ulysses.


2. A very small part of acting is that which takes place on the stage!


3. They belong to a different race. Their crudity is that which was of the Roman, as compared with the Greek, in real life.

I can kind of guess its usage, but I want to know more about this grammar structure. Searching on Google mostly gave me the simple difference between "that" and "which", and some examples using "that which":

1. that which we call a rose (from "Romeo and Juliet")


2. that which we persist in doing

It is a pity that Google search does not direct me to any useful page about "that which". Can someone explicate its grammar for me?

Answer

The combination of that which in the example sentences is fine. The that is a pronoun referring back to a noun phrase and the which is the relative pronoun used for non-animate antecedents. If we expand the shortest of the OP's example sentences to replace the pronoun that with its noun referent, we get:

• A very small part of acting is acting which takes place on the stage!

We can see a similar (personal) pronoun / relative pronoun combination in:

• He who hesitates is lost.