to who vs who to?

[keannu]

I couldn't explain to my student when he asked me why 1 doesn't work, while 2 works. When a preposition comes before who, it doesn't work, while the latter works. I told him it's just idiomatic, inexplicable, but do I need to explain this? Can you explain why?

ex1) I met the boy to who I gave the book.(x)
ex2) I met the boy who I gave the book to.(0)

[5jj]

If you are going to put 'to' before the relative, it needs to be 'to whom'.

[keannu]

If you are going to put 'to' before the relative, it needs to be 'to whom'.

I know it, but they are curious why "to whom" works, while "to who" doesn't. There's no reason like why human beings have brains. Right?
Okay, a second thought tells me "whom" is objective, while "who" is subjective, but what confuses learners is that "who.......to" works.

[Barb_D]

It's because of the vanishing use of "whom" except when it comes immediately after a preposition.

You can change the "who" to "whom" in your second sentence and be perfectly grammatical. You just won't sound as natural (these days) as you would using "who."

I'm sure The Parser will jump in and urge you to use "whom" there but I'm afraid he's tilting at windmills in his efforts to get people to use pronouns according to the rules of yore.

[5jj]

I know it, but they are curious why "to whom" works, while "to who" doesn't. There's no reason like why human beings have brains. Right?

It's quite simple. For most users of BrE, 'whom' is dead. Also, most speakers of BrE naturally and happily send the preposition to the end; 'to who(m)' is used only rather formally; people who speak formally tend to use use 'whom' when it is appropriate.

On your second point, most speakers of BrE do not give a thought to whether 'who' functions as a subject, direct object or prepositional object.

ps. Barb got in there first.