The relativized element of a relative clause?

“Wh” and non-“wh” relative clauses - Page 5:

• “wh” relative clauses (“The bag which he put there was stolen.”)

• “that” relative clauses (“The bag that he put ______ there was stolen.”)

• bare relative clauses (“The bag he put ______ there was stolen.”)

In each of these three examples, there’s an anaphoric relation with the antecedent “bag”. In the first, it’s from the relative pronoun “which”; in the second and third, it’s not from any word that’s said or written. But in all three, “he put R there” is understood.

Each of the three has a relativized element. In the first, it’s overt (“which”); in the second and third, it’s covert.

It seems that that doesn't have an anaphoric relation with the antecedent bag. Also, in page 6, in the example of that relative “a computer [that ______ cost too much]” you can see there's a gap indicating the presence of the relativized element, as opposed to the example of which relative “a computer [which cost too much]” in which there is no gap because which is the relativized element.

Why is which a relativized element but that is not? Is it because of the informality of that?

Solution 1:

“wh” relative clauses (“The bag which he put there was stolen.”)

“that” relative clauses (“The bag that he put ____ there was stolen.”)

bare relative clauses (“The bag he put ____ there was stolen.”)

"That" cannot be R because it's a subordinator, not a relative word (it's the same subordinator that introduces declarative content clauses).

As your examples show, in that and bare relatives the relativised element is covert and represented by the gap notation '____'.