Their mistakes is what saved Snowden because otherwise he would be in prison now.

Source: The Putin Interviews by Oliver Stone

imho 'is' refers to the noun 'what' that is from the right side of the verb 'to be' that is quite unusual for me. Why does this verb take a form regardless of the noun that precedes it? Is it possible to use 'are' in this case?

ps I've seen the similar topic - Referring to a plural noun as singular? But it didn't help me to understand the usage

  • It's hard to see how this is not a duplicate. Are you a native speaker?
    – tchrist
    Jun 27, 2017 at 15:03
  • Possible duplicate of Agreement in "[Singular Noun] Is/Are [Plural Noun]"?
    – SteveES
    Jun 27, 2017 at 15:03
  • @tchrist I think the other duplicate more accurately reflects the Dirty Hippy's confusion
    – SteveES
    Jun 27, 2017 at 15:04
  • @SteveES Your link is to a question whose answers explain that a verb agrees not with its complement but with its subject. It doesn't include situations where notional agreement rules.
    – tchrist
    Jun 27, 2017 at 15:06
  • 1
    If this is a transcript of a live interview, it may well just be an error—our tongues get ahead of our brains sometimes when we're speaking, and things like tense agreement can get mixed up. These kinds of errors are usually corrected when writing up journalistic interviews (along with dropping out all of the uhs and ums and smoothing over sentence fragments and other disjointed statements), but they're very common in speech.
    – 1006a
    Jun 27, 2017 at 18:36

1 Answer 1


Your source is wrong.

Their mistakes are what saved Snowden

From https://books.google.com/books?id=4BMkDwAAQBAJ&pg=PT59&lpg=PT59#v=onepage&q&f=false

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