mains is essentially unedited. As

most readers will know, David

Cass has collaborated extensively

with Karl Shell over the years.

We met with Dave in his of¬ce

at the University of Pennsylvania™s

Economics Department just

before noon. Amid the boxes

and piles of articles, books, and

CDs, he sat in his standard jeans

and T-shirt, looking about as

disheveled as he usually does. We

chatted there for a while, went out

Figure 2.1 David Cass, June 3,

and continued over lunch, and

1994, on the occasion of receiving an

then returned to complete the

honorary degree (“docteur ès sciences

economiques honoris causa”) from interview several hours later. It

the University of Geneva. was an unseasonably warm day in

February, and Friday the 13th to

be exact. That is traditionally an unlucky day, but one that turned out in

this case to be a real treat, at least for us! We hope that you get as much

out of this conversation with Dave as we did.

MD (Macroeconomic Dynamics): Let™s begin by talking about

graduate school and your adviser, [Hirofumi] Uzawa. How did you ¬rst

hook up with him?

Cass: Okay. I viewed Stanford™s graduate program as being completely

chaotic. I™ll give you an example. The ¬rst year I went to Stanford, they

had a qualifying oral in the ¬rst semester and everybody had realized that

this was patently absurd. So they had abolished the requirement, but

they™d scheduled the orals already, so they decided to hold them. My

oral”and I didn™t even know people on the Stanford faculty very well at

the time”my oral was composed of Ken Arrow and somebody else.

When I found out about Arrow, I was terri¬ed. So I went in and Ken

asked me a question and I gave some half-assed answer, and he has this

capability of taking someone™s answer and then reframing it in a way that

makes a lot of sense. So, my qualifying exams consisted of my short

responses to Arrow and then him elaborating to make sense of them.

34 Stephen E. Spear and Randall Wright

But the point is, they had this requirement that they abolished but they

scheduled, and that was typical. So basically, at Stanford you were kind

of left on your own as a graduate student. There was just no coherence

in the program. Now, I don™t remember exactly how I ¬rst met Uzawa,

but there was a mathematical economics group who had of¬ces separate

from the department in a little house on campus called Serra House, and

that is where what I consider the really good people at Stanford were:

Arrow, Uzawa , Scarf. We had other kinds of mathematical social scient-

ists there. And somehow, Karl [Shell] knew about Serra House right away,

and we had our of¬ces there.

MD: Did you and Karl enter in the same year?

Cass: Yeah, and somehow Karl introduced me to Serra House. I don™t

remember how we got involved with Uzawa, but we just got involved with

him. Maybe he ran a seminar or something. I don™t really remember how

we met, but it was clear that this guy was really into research and very

good at directing people, so we hooked up with him. Then, the last two

years at Stanford (I stayed four years), I basically spent at Serra House

working with Uzawa. He always had seminars going. Uzawa, in my view,

by conventional standards, is a terrible lecturer, but he is an awesome

teacher. His greatest virtue is that when he lectures he shows you how he

does research. If he doesn™t prepare, he will tell you about a paper he is

working on, and he gets up and basically re-creates the mistakes that he

made and corrects them. He explains why he decided to do this and that,

and it is just like you are taught by doing research.

So, I took a couple of courses from him and found them great, but

from conventional standards they were probably a disaster. He taught

econometrics, and he wanted to calculate some estimator, probably a

limited information maximum likelihood estimator, but he didn™t really

remember anything about it. Half of the course consisted of Uzawa

coming in and starting to prove a theorem about this estimator, and he

would go on for about an hour or an hour and a half, and then he would

realize that he had gone off on the wrong track again and he would say

“Oh, sorry.” Next time he would start up again”it was really incredible!

But it was interesting. He has a really good mind for working from ¬rst

principles and for working out how you solve a problem.

Uzawa was a marvelous person to work with. I model my career in

terms of working with graduate students after the experience I had work-

ing with Uzawa. He treats them exactly as equals and he spends a hell of

a lot of time one-on-one with them in all kinds of situations. Don™t think

it was only in the of¬ce”it could be going to a bar, or any of that. He

just spent an enormous amount of time. Now Uzawa probably never

read anything that I wrote. I am sure he didn™t. But he always wanted to

An Interview with David Cass 35

talk about it. He™d always force his students to deal with that, and he had

a group of students in seminars, so that all the students knew what the

other students were doing. Of course, we had a focused subject”growth

theory and, more particularly, applications of a fancy version of the

calculus of variations, the maximum principle, to growth models. So we

all had a common background but, actually, that personal thing is one of

the reasons I got into trouble with the Penn administration. One of the

basic issues I had about dealing with graduate students here was that

somehow the administration wanted me to distinguish very carefully

between my professional activities and my social activities, and I told

them that wasn™t consistent with my idea of how you deal with graduate

students, and it isn™t. So this is all in response to the question of how

did you meet Uzawa”and the actual details about meeting Uzawa I do

not remember.

MD: Did you know that you wanted to do growth theory?

Cass: Not at all.

MD: What was your undergraduate training?

Cass: I was a joint Economics“Russian Studies major.

MD: Russian Studies?

Cass: Yeah. Very anomalous because languages were probably my

weakest suit.

MD: Where was that?

Cass: The University of Oregon. I always thought that I was to become

a lawyer because that™s a tradition in my family. I spent a year at the

Harvard Law School and hated every minute of it. I spent most of my

time re-reading great Russian literature, and I learned how to answer

exams just by deductive logic. I™d memorize a few de¬nitions and go

from there, which got me through. Then I went in the army and I

decided that what I really wanted to do was to go back to graduate

school in Economics, and I decided to stay on the West Coast. I was

very lucky. I didn™t know anything about graduate schools but it seemed

like the major choices were Berkeley and Stanford. Just by chance I

decided Stanford rather than Berkeley, and I think it was a hell of a

good decision, because the faculty that I got inspired by are really

world class.

MD: So why did you decide to go to graduate school in economics?

Cass: I liked economics, and I realized that my undergraduate degree

was the tip of the iceberg. They were just barely getting into the use of

equations in class and it was kind of fascinating to me”the idea of being

formal about a social science.

MD: So you probably had very little mathematics training when you

went to grad school.

36 Stephen E. Spear and Randall Wright

Cass: I had virtually no math training. I had taken college trig, algebra,

geometry, and that was it. In fact, I remember the ¬rst day of class at

Stanford there was a guy teaching a macro course; his name was Bob

Slighton. The ¬rst day of class he wrote down a general equilibrium

model and decided that he was going to calculate a multiplier, which is

just a derivative of the model. He ¬lled the blackboard in the front of

the room and the side of the room and I didn™t understand a word

of this. I knew what a derivative was but I didn™t know what a partial

derivative was. He was doing all this partial differentiation. Of course, in

those days, in terms of partial differentiation, people didn™t really under-

stand what they were doing. They would write down differential forms,

what in differential topology are called the tangent spaces, and they™d

be dealing with calculus on manifolds but didn™t really understand it.

The technique was kind of incomprehensible.

I went home from that class and I said, “Well, you™re not really pre-

pared to sit in graduate classes in economics,” so I basically re-registered

for calculus and statistics and I think I sat through Slighton™s class, which