[blacknomi]

Originally Posted by Casiopea

Originally Thursday was Thor's Day, which later on became a compound. I don't know if speakers today view the days of the week as compound forms, but historically Thursday was an adjective+noun structure, and hence the use of an interrogative adjective.

What day? Thursday. (interrogative adjective)

An interrogative adjective may look like an interrogative pronoun, but it is used differently in the sentence: it is an adjective, used to modify a noun or pronoun, whereas an interrogative pronoun is used to represent a noun.

Interrogative Adjective: 'What' modifies 'day' (modification)
What day is it? It is Thursday (historically, Thor's Day).

Interrogative pronoun: 'What' stands for 'date' (replacement)
What is the date? The date is November 21st. (Predicate nominative, not adjectival)

*What date is it? (Interrogative pronoun)
Error: Structural
There are two subjects. What stands for 'date'; e.g., *Who John is it?

Repair: What is the date? (What = the date)

*What date is it? (Interrogative adjective)
Error: Semantics
What modifies 'date', giving *What kind of date is it? November 21st is not a kind of date. It is a date.

Repair: What is the date. (What = the date)

I ask my best friend, Google, to search "What date is it." Here's an interesting link I think it might be authoratative.
http://www.bbc.co.uk/schools/primary...on_flash.shtml

Is it okay in BE?!