whereof

know whereof (one) speaks

formal To be knowledgeable about or familiar with what one is saying. Yes, I know whereof you speak, though I have yet to deal with such a situation myself. Oh, don't pay attention to that old fool. He knows not whereof he speaks.
See also: know, speak, whereof
Farlex Dictionary of Idioms.

know whereof one speaks

to know well the subject that one is speaking about. You are wrong! You do not know whereof you speak. He simply doesn't know whereof he speaks.
See also: know, one, speak, whereof
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • know whereof (one) speaks
  • know whereof one speaks
  • know like a book, to
  • know (one's) beans
  • know a trick or two
  • familiar
  • familiar with
  • familiar with (someone or something)
  • know about
  • know about (someone or something)
References in periodicals archive
"The acquisition price is USD47m, whereof USD33m shall be financed through debt and USD7m will be paid in cash.
Orexo said that it has acquired all US rights for Abstral from ProStrakan and will receive SEK610m, whereof SEK248m was paid in June 2012.
. 'Why the country should not face bankruptcy whereof the sitting Prime Minister deliberately helps a NAB accused Finance Minister flee from the country in his official plane?
Having spent much of his adult life as a politician, the President must know whereof he speaks.
Sales for the quarter increased by 12% in local currency, whereof 4% comprised organic growth.
In the written verdict, the apex court observed that additional attorney general confirmed that, the inquiry in the case was initiated by the FIA in the year 2014, which was concluded in December, 2015, on the basis whereof formal FIR was registered on December 15, 2015.
In the written verdict, the apex court observed that additional attorney general confirmed the inquiry in the case was initiated by the Federal Investigation Agency (FIA) in 2014, which was concluded in December 2015 on the basis whereof a formal FIR was registered on December 15, 2015.
The measures will lead to restructuring charges in the first quarter 2019 of approximately SEK 1B, whereof approximately SEK 300M will have a cash flow impact.
Currently, the total number of shares in Alimak amounts to 54,157,861, whereof zero own shares are held by Alimak as on 5 December 2018.
The CDA's report on the layout plan of Bahria Town alleged that the 'Bahria Town is carrying out development work in Bahria Enclave (extension, almost 03 times larger in size, layout plan whereof has not been approved).'
The political parties, candidates and election agents have been asked to abide by all directions, instructions and regulations issued by the Election Commission, from time to time, relating to smooth conduct of elections, the maintenance of public order and morality and refrain from maligning the Election Commission in any form whatsoever, violation whereof would entail contempt as contemplated in Section 10 of the Election Act 2017.