This sentence is interesting to me:
I don't know what you know.
It seems ambiguous. It has two possible meanings. It is so ambiguous that I'm actually struggling a bit to explain the differences without using ambiguous wording, as even context does not always bring clarity to this sentence:
It could mean that I am acknowledging that you have knowledge that I don't have. For example, "You are an expert. I am a novice. I don't know what you know." In that case "what" seems to be referring to the knowledge itself.
It could also mean that I am unaware of the collection of things that you are knowledgeable about. For example:
- I give an explanation that is unnecessary, as you already know the reasons.
- You: "I already know that, you don't need to explain."
- Me: "I don't know what you know. I explained it just in case."
It also doesn't necessarily seem specific to this form. "I don't know the things that you know" has a similar ambiguity.
The above two differences are similar to the differences between (respectively):
- I don't have what you have.
- I don't know what you have.
Or, I guess, in general: "I don't X what you X" vs "I don't know what you X". The ambiguity arises when X is "know": The two constructions end up identical.
So, I have two questions:
What is the source of this ambiguity? In particular, is the sentence ambiguous because I have learned to take grammatical shortcuts when using it (that is, is "I don't know what you know" grammatically incomplete, thus leading to ambiguity)?
What is the difference between the two readings of this sentence? Does the "what" serve as a subtly different part of speech, for example? Or, considering the "I don't ____ what you have" parallels, perhaps the differences are in the "know"s? It's almost like the first "know" in the second meaning of "I don't know what you know" is subtly different than the other three "know"s.