“An economist is a man who states the obvious in terms of the incomprehensible” is a popular economics saying of uncertain authorship. American agricultural economist Donald “Don” Paarlberg (1911-2006) said this in Great Myths of Economics (1968), as quoted in a newspaper book review published in November 1968.
 
American publisher Alfred A. Knopf Sr. (1892-1984) was credited with the saying in December 1969. Knopf—who was not an economist—is usually given credit for the saying.
   
     
Wikipedia: Don Paarlberg
Donald “Don” Paarlberg (June 20, 1911 – February 14, 2006) was a farmer, author, professor of agricultural economics, and a coordinator of the Food for Peace program.
   
OCLC WorldCat record
Great myths of economics
Author: Don Paarlberg; Principles of Freedom Committee.
Publisher: [New York] New American Library [1968]
Edition/Format:   eBook : Document : English
 
25 November 1968, Gaffney (SC) Leader, “New Books,” pg. 4, col. 1:
The Great Myths of Economics by Don Paarlberg. A general review of economic theories intended for the layman because the author charges that too many economists state “the obvious in terms of the incomprehensible.”
 
27 December 1969, Anderson (IN) Herald, “Folklore” by William Wade, pg. 4, col. 6:
“An economist is a man who states the obvious in terms of the incomprehensible.”—Alfred A. Knopf, AMerican book publisher.
 
2 September 1971, The Express (Lock Haven, PA), “Daffynitions,” pg. 4, col. 6:
ECONOMICS: Stating the obvious in terms of the incomprehensible.
 
27 October 1974, Atlanta (GA) Journal-Constitution, “Lou’s News” by Lou Erickson, pg. 22-A, cols. 5-6:
My friend’s philosophy differed from the government economists. He did not state the obvious in terms of the incomprehensible.
 
16 January 1975, Albuquerque (NM) Journal,  “Journal Action Line” by C. Ward Fenley and Louise Miller, pg. A-5, col. 5:
Q. After listening to Pres. Ford and all those wacky COngressmen on cure for our economy, I am reminded of that definition of an economist who talked about things neither he nor his listeners could understand. Who gave us that definition?—A.H.
 
A. Whether he gave the definition you are seeking, I have no way of knowing, but it was the great publisher, Alfred A. Knopf who said “an economist is a man who states the obvious in terms of the incomprehensible.”
     
26 December 1993, Chicago (IL) Tribune, “Fast Track” by Cheryl Lavin, pg. 8:
“An economist is a man who states the obvious in terms of the incomprehensible.” -Alfred A. Knopf
 
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“An economist is a man who states the obvious in terms of the incomprehensible.”
-Alfred A. Knopf, wb 115 today
8:59 AM - 12 Sep 2007
 
Google Books
The Biteback Dictionary of Humorous Business Quotations
By Fred Metcalf
London: Biteback Publishing Ltd
2014
Pg. ?:
An economist is a man who states the obvious in terms of the incomprehensible.
Alfred A. Knopf, American publisher
 
Google Books
Scorn:
The Wittiest and Wickedest Insults in Human History
By Matthew Parris
London: profile Books Ltd
2016
Pg. ?:
An economist is a man who states the obvious in terms of the incomprehensible.
Alfred A. Knopf