Have a look into these two sentences:

  1. I am waiting for what I don't know.
  2. I am waiting for I don't know what.

My question is:

(a) Is there any difference in meaning between #1 and #2?
(b) Which one is correct and why? Please explain grammatically.

  • This is a very good question that deserves an upvote.
    – Kaz
    Dec 21, 2013 at 23:09
  • @Kaz Good point. I agree, and I've joined the upvote club!
    – user230
    Dec 22, 2013 at 8:33

3 Answers 3


Your first example, "I am waiting for what I don't know", is an unlikely construction; it could be used to say that there is some piece of information which you lack, and you are waiting to receive it. It's equivalent to What I don't know is what I'm waiting for.

I'm sorry I haven't finished the report. I am waiting for what I don't know: the final costs from Stepney. Once I've got that I can let you know where we stand.

Your second example, "I am waiting for I don't know what", says that you are waiting for something but you don't know what it will turn out to be. It's equivalent to I don't know what I'm waiting for.

I am waiting for I don't know what: maybe a contract, maybe bankruptcy, maybe a loan. John just told me to wait.

However, the first sequence of words could, if rephrased in speech or re-pointed in writing, be equivalent to the second example:

I am waiting—for what, I don't know.

  • Sans the extra punctuation, “I am waiting for what I don't know” has a Zen-like feel to it. It reminds me of that line from Dust in the Wind: “And if I claim to be a wise man, it surely means that I don't know.”
    – J.R.
    Dec 21, 2013 at 22:03
  • 1
    @J.R. Or the line attributed by Cicero to Socrates, "I know one thing: that I know nothing." Dec 21, 2013 at 22:49

The interesting thing here is that the "wh-clause" "what I don't know" can be hypothesized to be derived from the canonical sentence "I don't know what", which happens to be the other one you're asking about. Yet the meaning is different.

The difference is in the position of the wh-word. In wh-clauses, the wh-word--such as who, what, or when---moves to the front. If it doesn't move to the front, then you do not have a wh-clause.

So, "what I don't know" is a wh-clause, whereas "I don't know what" isn't.

The wh-clause is a nominal clause which denotes whatever the wh-word refers to. "I'm waiting for what I don't know" is somewhat nonsensical, but it has a valid grammatical form. We can make a very similar sentence which makes sense:

I want to learn what I don't know.

The "what I don't know" wh-clause serves as a noun, denoting that which I don't know (and that is what I want to learn).

On the other hand:

I'm waiting for I don't know what

is an instance of transformation; perhaps extraposition. (The extraposition examples resemble this situation). That is to say, we can regard it as a rearrangement of the canonical sentence, where the "I'm waiting for" part moves to the front:

I don't know what I'm waiting for.

Note that in this sentence, the "wh-clause" is "what I'm waiting for", not "what I don't know"

So basically the difference between your two sentences is the role of what. In one it is "what I don't know" and in the other it is "what I'm waiting for" (rearranged by a transformation which moves the "I'm waiting for" part away from "what" out to the front of the sentence).

Lastly note that although "I'm waiting for what I don't know" is nonsensical (how can you wait for something that you don't know?), the same words in the same order can express this:

I'm waiting. For what, I don't know.

This has the same meaning as "I don't know what I'm waiting for", or "I'm waiting for I don't know what", or "I'm waiting; I don't know for what".

  • Thank you Kaz. What a nice explanation in plain language. Thank you once again. Dec 23, 2013 at 14:11

The first sentence approaches correctness (and equivalence to the second one) if you punctuate it as

I am waiting; for what, I don't know.

which, in turn, is basically a compact form of

I am waiting.  For what?  I don't know.

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