Is the word order in "know what's what" correct?

Question

There's an expression: "to know what's what", as in: "He's been around for a long time - he knows what's what." (ref: Cambridge Dictionary).

But recently I started wondering: isn't it an embedded question? If so, shouldn't it actually be: "He's been around for a long time - he knows what what is."?

Answer 1

To clarify syntax, I will mark subjects with _s in this answer. I will follow the usual convention of marking unacceptable sentences with a preceding *.

The word order in "He knows what_s is what" is correct and does not have any subject-auxiliary inversion: the subject (the first what) comes before the auxiliary verb is, which comes before the predicative complement (the second what).

Syntax of interrogative clauses with multiple wh-words

"He knows what_s is what" contains two wh-words in the same clause: one as the subject, and one as the predicative complement (as MarcInManhattan rightly notes).

The use of more than one wh-word in the same clause like this is not common in formal language, but when it occurs, more than one wh-word can't be put at the start of the clause, so any additional wh-word(s) beyond the first stay in place rather than undergoing wh-fronting. In this case, the predicative complement what stays in place (or "in situ"). This is normal English grammar for this context; it is not exceptional.

Per Glottopedia's article on wh-in-situ:

in languages with overt movement of one wh-element (like English), the other wh-elements stay in situ.

In the case of what_s is what, since the clause has a wh-word as its subject, no subject-auxiliary inversion is possible, whether the clause is embedded or not (compare Who_s did it? I don't know who_s did it, not *Did who_s it? or *I don't know did who_s it?).

We do see subject-auxiliary inversion (with do-support if needed) in a non-embedded interogative with multiple wh-words where the first wh-word is not the subject: "What did he_s put where?" And when embedded, we would have wh-fronting without subject-auxiliary inversion as "I don't remember what he_s put where."

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A priori, we might suppose that it should be syntactically possible to front the predicative complement, and leave the subject what in situ, which would result in it inverting with the verb. That would create "What is what?_s" and when embedded, "What what_s is". But I don't think this actually sounds natural to any speakers, so I don't think that is the structure that is actually used in the expression "know what's what".

In practice, there seem to be restrictions in interrogative clauses with multiple wh-words on which ones can be fronted.

These restrictions seem to be called "superiority effects"; here is a quote from literature studying that topic in a different context:

for speakers that do allow wh-extraction of indirect objects, the predicted contrast does appear to hold, as shown in (85a-b).

(85) a. ?? Whom_i did John give t_i what?
b.* What_i did John give whom t_i?

(Symmetry in Syntax: Merge, Move, and Labels, by Barbara Citko)

Other analogous examples

Other examples of the same type: "I don't know who_s did what" and "I don't know what_s goes where" (because the subjects are who and what respectively, the additional wh-words what and where remain unfronted).

Note that this word order is much more acceptable than "*"I don't know what who_s did" or *"I don't know where what_s goes."

Answer 2

The word order is correct.

Other people may parse this differently, but one way is to consider "what's what" as a nominal clause (functioning as the object of "know"). The first "what" serves as the nominal clause's introductory word (subordinator). It also functions as the clause's subject, so the rest of the clause follows in regular order: the simple predicate ("is") comes next, followed by the predicate nominative (the second "what").

It is a bit unusual for both a subject and a predicate nominative to be wh-words, but in this case it is idiomatic.

By the way, it is also possible to write "he knows what what is", but in that case the first "what" would be the predicate nominative and the second "what" would be the subject. The meaning would therefore be slightly different and wouldn't seem to make much sense (although it might in some contexts).

Answer 3

Yes, because in short, you know, what is what. 'know what is what' is the correct order of words. No order of words would make any sense.

For example, what^2 would be what you know is. what^1 is regular usage.