If I understand Humberto's and Thomas's posts correctly, the simple 
answer is "tradition" or "precedent." There is, I think, a more 
penetrating answer.

It is that the goal of this framework has been to teach about scarcity.

Marshall used the demand and supply framework as an analogy, in my 
interpretation. Having been trained in mathematics, he found more uses 
than others. In his framework, what is scarce is quantities of objects 
-- assumed quantities of homogeneous consumer goods and factors of 
production. Scarcity refers in this scheme to a quantities in relation 
to the valuations placed by demanders. Since quantities of things are 
typically arranged by people who are subject to the law of gravity, 
while values are abstract mental phenomena, the analogy seems easier to 
communicate by putting quantity on the horizontal axis.

In other words, beginning economics students count quantities by lining 
them up horizontally (as preschoolers who arrange their dolls and 
soldiers on the table). They conceive of values abstractly. If you want 
to communicate scarcity by means of a relationship between quantity and 
values to students, it seems more efficient to do so in the way that has 
become traditional.

Not all scarcity can be represented by this means. Scarcities of study 
time, of capital, of NFL quarterbacks, of a work of art, of healthcare 
or healthcare insurance, etc. do not seem worthwhile treating by means 
of the demand supply framework. The framework is also ill-equipped to 
show how the problem of scarcity is dealt with by individuals under 
market economy conditions by means of a division of labor and how it is 
dealt with by the isolated actor or central planner.

In the Walrasian, or GE system, these curves emerge as being 
simultaneously determined, as Tony observed. They represent scarcity by 
assuming fixed objective factors of production in relation to preference 
functions in a multi-dimensional system. However, no teacher who I know 
tries to communicate scarcity to her class in this way. Although I have 
never had a class in this subject, I assume that the GE system is mostly 
taught for other purposes.


On 2/2/2011 10:31 PM, Steve Horwitz wrote:
>
> Folks,
>
> It’s been a long time since I looked at this issue, so I’m going to 
> rely on the wisdom of this wise crowd.
>
> What is the most accepted explanation for why we have the independent 
> and dependent variables reversed in supply and demand graphs? It came 
> up in class today and I gave “an” answer, but I admitted to my class 
> that I wasn’t confident that I was correct. I also promised them I’d 
> ask all of you.
>
> So what’s the consensus in HET on this issue?
>
> Thanks.
>
> Steve
>
> --
>
> Steven Horwitz
>
> Charles A. Dana Professor and Chair
>
> Department of Economics
>
> St. Lawrence University
>
> Canton, NY 13617
>
> Tel (315) 229 5731
>
> Fax (315) 229 5819
>
> Email [log in to unmask] <mailto:[log in to unmask]>
>
> Web: http://myslu.stlawu.edu/~shorwitz
>

-- 
Pat Gunning
Professor of Economics
Melbourne, Florida
http://www.nomadpress.com/gunning/welcome.htm