Prepositional complement (two - part question)

Question

In grammar, a subject complement follows a copular and describes the subject of a clause. Although nouns, pronouns and noun phrases most frequently perform the function, prepositional phrases can also function in the say way.

1) Can a prepositional phrase beginning (or ending) with 'to' follow a copular to indicate directions? If so, under what circumstances? For example, I don't believe it is grammatically sound to ask:

• Which train is to the city? (to ask for the train that will going in the direction of the city)

or

• Is this letter to John?

or

• Where are you to? (wouldn't be correct without 'off' before the 'to')

If they are indeed ungrammatical, why so? Why does 'to' strictly need a verb before it when 'from' doesn't despite their falling under the same category of words?

2) Whether the usage of prepositional phrases as subject complement is acceptable can greatly vary depending on the context. For example, it's perfectly grammatical to say:

• I am on all fours looking for my keys.

But what if the verb "BE" is behaving as a lexical verb, taking do-support in a present-tense negative construction?

• "Don't be on all fours, the ground is really dirty," said...

Is it still correct? If not, is there any way can I rephrase it without adding implications? Another example:

• "Don't be in this room!"

Many thanks in advance for answering.

Answer 1

In short, YES and YES.

Regarding question #1, it's fine to say the following:

This train is to Memphis.

This letter is to John.

Even these, using an infinitive of purpose (the latter is in the passive voice and can also be read to mean a plan, not just an intent):

This bathroom is to use when the other isn't working.

This bread is to be eaten.

Like the bread example, we can also say:

You and I are to leave at 5 tomorrow morning.

These are fine because the prepositional phrases are actually adjectives, modifying the noun.

You used the term "copular" for a form of "be", which your examples include. It's less likely to use these "to" phrases with a non-be copular verb, as in the following examples:

That train looks to Memphis.

This letter looks to John.

More likely, one might express these as:

That train looks like it's to Memphis. / That train looks to be to Memphis.

That letter looks like it's to John. / That letter looks to be to John.

I don't know a rule for this, but I think that it's just an avoidance of the ambiguity when using a copula verb which could be followed by a directional prepositional phrase, modifying it as an adverbial phrase. Maybe it just hasn't caught on over all these years because there are simpler ways to say it.

Regarding #2, your examples are all fine with "be".

You can do contortions and still be safe:

If you'd put Fred's address on it instead, then the letter wouldn't really have been to John, would it have?

Well, according to the address it would have been going to be to Fred, but the letter inside still would have been to John!

Funny that you mention Fred, because my next letter is going be to him.

I hear that Fred has bought a new wastebasket. It's to put all your letters to John into.

Answer 2

1. Is this letter to John? - is perfectly fine and grammatically correct. (MacMillanDictionary) The only difference is between for and to:

   • for mostly means "meant for"
   • to mostly means "addressed to"

There's "Here's to + somebody" if you want to make a toast to someone.

"To" is mostly followed by a verb in the case you are speaking of, sometimes it if followed by a gerund or a noun (mostly in informal English).

2. Where are you to? - is very informal and slang.

   • Welsh expression for "where is it?" or "where are you?"
   • Bristolian slang/expression for "where is it", "where are you" and "whereabouts".
   • Cornish expression for "whereabouts" or "where is it". basically means "where".

3. Which train is to the city? - this is also very informal and ungrammatical. As a non-native I can still understand the meaning of this sentence.