Learn English – What’s the exact usage of “that of”

possessives

I think in the following sentence:

Adam's answer was similar to that of clergy.

"That of clergy" can be replaced by "clergy's" or "clergy's answer":

Adam's answer was similar to clergy's.

So, if my understanding is correct, can we say the following two sentences are grammatically equivalent too?

This is my book.
This book is of me.

Since in the first sentence, "of clergy" was indicating possession, I expect "of me" to mean "mine" and indicate another form of possession too.

Best Answer

That of is unnecessary when the comparison is to a single noun and you can use an apostrophe:

  • Adam's problem is similar to John's.

You can probably also get away with it for a two-word noun phrase:

  • Adam's problem is similar to his friend's.

But you need it for longer noun phrases. So, we don't usually say:

  • Adam's problem is similar to the majority of people in the western world's.

but:

  • Adam's problem is similar to that of the majority of people in the western world.

The following sentence is problematic:

  • Adam's problem is similar to the majority of people in the western world.

because it is not the case that problem and the majority of people in the western world are similar entities.

Addendum:

That is a pronoun whose referent in this case is problem. Of course, if the referent is a plural noun, then that changes to those:

  • Adam's problems are similar to those of the majority of people in the western world.
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