what he knows is wrong

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Senior Member
Let's say Professor X reads outdated books or those with inaccurate information, while John Doe reads up-to-date books with reliable information. Please confirm if the phrase what he knows is wrong sounds natural.

Joe: Professor X happens to be listening while I was at the library. He corrected me when I asked the librarian, "Can I borrow books?" He told me that I should have used may instead.​
John: What he knows is wrong. Modern usage guides now accept can in informal situations.​

Joe: Professor X told us that Einstein failed math.​
John: What he knows is wrong. In his book, "Einstein: His Life And Universe," Walter Isaacson wrote about Einstein’s response to the Ripley's claim: “I never failed in mathematics. Before I was 15 I had mastered differential and integral calculus.”​
  • entangledbank

    Senior Member
    English - South-East England
    No, if you use the word 'know', you are committed to saying it is a fact. That is, if you say, 'Jim knew Einstein failed maths', that logically implies you also believe Einstein failed maths. (Words with this property are called 'factive'.) So you have to talk about what someone believes if you don't also believe it.

    :cross:I used to know that, but I found out I was wrong.
    :tick:I thought I knew that, but I found out I was wrong. [your belief that you know is only a belief - it can be wrong]


    Senior Member
    English - Southern England
    You could use "That / What he said / What he told you /He is wrong.

    But I would only use "What he knows.." if the verb "to know" had been used earlier. e.g. A. I know it was Amy who ate the cake. B. What you know [What you thought you knew] is wrong. John confessed yesterday."
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