Notwithstanding Marshall's remarks in his famous 1906 letter to
Bowley, he kept including a un-burnt Mathematical Appendix in
successive editions of his Principles of Economics.

Quoting "E. Roy Weintraub" <[log in to unmask]>:

> Kwasnicki's appealing to Marshall's letter to Bowley in this argument about
> mathematical modeling today is like appealing to Bishop Ussher on the
> fossil record. Marshall was unable to understand the mathematics of 1906,
> which was not the mathematics of his youthful success as Second Wrangler.
> For documentation, see my (2002) How Economics Became a Mathematical
> Science, pp. 17-25 (Chapter 1, "Burn the Mathematics (Tripos)".
>
> On Sat, Nov 15, 2014 at 8:34 PM, Witold Kwasnicki  
> ><[log in to unmask]> wrote:
>
>>  It would be good to keep in mind the wisdom of Alfred Marshall (which
>> may be considered as a message to all mathematical economists).  In his
>> Principles of economics he wrote:  "? Nature's action is complex; and
>> nothing is gained in the long run by pretending that it is simple, and
>> trying to describe it in a series of elementary propositions ... The chief
>> use of pure mathematics in economic questions seems to be in helping a
>> person to write down quickly, shortly and exactly, some of his thoughts for
>> his own use: and to make sure that he has enough, and only enough, premises
>> for his conclusions? (Marshall, 1930, p. x-xi).
>>
>> In the 1906 letter to A.L. Bowley, (after Guillebaud, *Marshall?s
>> Principles of Economics*, Vol. 2. (Notes), p. 775.) Marshall wrote:
>>
>> ?I had a growing feeling in the later years of my work that a good
>> mathematical theorem dealing with economic hypotheses was very unlikely to
>> be good economics, and I went more and more on the rules:
>>
>> (1)  Use mathematics as a shorthand language, rather than as an engine of
>> inquiry.
>>
>> (2)  Keep these till you have done.
>>
>> (3)  Translate into English.
>>
>> (4)  Then illustrate by examples that are important in real life.
>>
>> (5)  Burn the mathematics.
>>
>> (6)  If you can?t succeed in (4), burn (3). This last I did often.?
>>
>> Best regards,
>>
>> Witold Kwasnicki
>>
>>
>>
>>
>>
>>
>>
>>
>> W dniu 14-11-2014 23:25, Birks, Stuart napisa?(a):
>>
>> Uskali makes a good point.
>>
>> If you frame the issue in terms of theories being possible   
>> analogies, as several economists have suggested, the concern   
>> disappears. If you say, "He swims like a fish", you do not have to   
>> believe that he is a fish. The analogy is simply giving a   
>> representation and possible insight into how he swims. Similarly   
>> with theories, they may sometimes provide some insight or   
>> understanding of real world phenomena, but, as analogies, they   
>> cannot be considered as 'true' descriptions of the real world. Any   
>> belief that they are is misplaced.
>>
>> -----Original Message-----
>> From: Societies for the History of Economics [mailto:[log in to unmask]]  
>> On Behalf Of Uskali Mäki
>> Sent: Saturday, 15 November 2014 10:08 a.m.
>> To: [log in to unmask]
>>
>> Subject: Re: [SHOE] MARK BLAUG AND BELIEF IN MODELS
>>
>> I would say one is not compelled to make a choice between use and   
>> belief, so no sharp dichotomy here. Depending on the intended or   
>> justified use of a model, and on how good the model is, one is   
>> permitted or even advised to believe some parts or aspects of the   
>> model (insofar as its relations to its target are concerned).   
>> Models are far more complex creatures than what most practicing   
>> economists or historians or methodologists of economics have been   
>> able to clearly articulate. Mark Blaug's concern is one that   
>> troubled economists of the 19th century already.
>> c uskali mäki
>>
>>
>> Lainaus Bruce Larson <[log in to unmask]>:
>>
>> Here is the Theil quote, which I always use on the first day of my
>> intermediate microeconomics course: "It does require maturity to realize
>> that models are to be used but not to be believed." Henri Theil,
>> *Principles of Econometrics* (1971), p. vi Bruce Larson University of North
>> Carolina at Asheville On Thu, Nov 13, 2014 at 11:21 PM, David Levy <
>> [log in to unmask]> wrote:
>>
>> There is a "joke" in Henri Theil's Principles that models are to be used
>> not believed. Around page 7 or so ... My copies are at the office but maybe
>> I can find this on the web. I looked into years ago ... but let me not rely
>> on my memory. David On Thu, Nov 13, 2014 at 7:08 PM, Richard Lipsey <
>> [log in to unmask]> wrote:
>>
>> My late good friend, Mark Baugh, was wont to say that the problem with
>> economists when they came to talk about the real world was the they
>> believed their own models. I heard him say something like that many times
>> but never saw it in print, although I suspect he did commit it to print
>> somewhere in his voluminous writings. I am writing an essay that amply
>> illustrates Mark's comment and would like to quote him on the opening page.
>> I would be most grateful if anyone could help we with a reference to where
>> Mark made that comment, or something similar, in print? Richard Lipsey
>>
>> -- David M. Levy Professor of Economics George Mason University Fairfax VA
>> 22030 703-993-2319
>>
>>  --
>> --
>> Uskali Mäki
>> Academy Professor
>> TINT Centre of Excellence in the Philosophy of the Social Sciences   
>> Department of Political and Economic Studies University of Helsinki  
>>  http://www.helsinki.fi/tint http://www.helsinki.fi/tint/maki   
>> [log in to unmask]
>>
>>
>
>
> --
> E. Roy Weintraub
> Professor of Economics
> Fellow, Center for the History of Political Economy
> <http://hope.econ.duke.edu/>
> Duke University
> www.econ.duke.edu/~erw/erw.homepage.html
> https://www.facebook.com/FindingEquilibriumDuppeWeintraub
> <http://press.princeton.edu/titles/10206.html>
>