Joseph Kohn – US mathematician who’s never forgotten Prague


2008 has been a year of anniversaries linked to milestone events which changed the course of Czech history – 1968, 1948 and 1938. In those years, many Czechs left their country due to the deteriorating political situation – an imminent war, a communist takeover and a Soviet-led invasion. Our guest in this edition of One on One is Joseph Kohn, a native of Prague, who left Czechoslovakia in 1938, and who is now a professor of mathematics at Princeton University in the United States.

Joseph KohnJoseph Kohn “I left when I was seven years old but I remember things quite clearly. When I returned for the first time to visit in 1961, I could find my way home, to our house, from Petřín. And in general, I remember things and impressions I had then. I remember clearly when the hostilities started before the Munich Pact, how there were blackouts, and from our house we could see the German sympathizers lighting flares in defiance of the blackout. I remember the nervousness of everybody, and I remember vacations in Krkonoše, and many other little things.”

What did your parents do?

“My father was a well-known architect here; he designed some of the buildings on Letná, that series of apartment houses, and many others; he especially did reconstructions of many older buildings here, and also some villas, both in and outside of Prague, especially near Česká Lípa.”

Your family left in 1938. Was it difficult to get out?

“Well, we actually left in 1939, when it was already very difficult to leave. But fortunately, I had an uncle who was very aware of the danger of staying. He managed to get visas for my whole family on my father’s side, which consisted of 21 people, and we got it to Ecuador. The ambassador of Ecuador was very sympathetic to the question of Jews emigrating and we were able to go there.

I imagine it must have been a big change, moving to Ecuador from Prague.

It was a tremendous change. The positive part was that people in Ecuador were very friendly. We, the Jewish emigrants filled a big gap because there was hardly any middle class. The country was developing in many ways. Most people were illiterate peasants, almost or completely Indian, and then there were the absentee landlords, so the middle class was really needed there and filled that gap. Most of the immigrants had great opportunities there. So from that point of view it was easy. But on the other hand, there was of course a big cultural difference, which wasn’t so easy.

When did you move to the United States?

“We came to the US immediately after the war. We stayed in Ecuador from 1939 to 1945.”

You are a well-known mathematician, a professor of maths at Princeton. What made you choose this career?

“I enjoyed many things but I found mathematics fascinating and easy, and I was always interested in mathematics and physics and the philosophical questions around the two subjects. I went to high school in New York and than I went to MIT, and in my first year there I had to decide which direction I will go. I was deciding between mathematics and physics but the first year physics lab were very routine and boring and so I decided to skip that and went for mathematics.”

Was it difficult to stay in the field after you graduated?

Actually, it was not difficult at all because I had the good luck of graduating, of getting my PhD in 1956. And in 1957, there was a complete revival of science in the United States because of the advent of the Sputnik. There was a feeling in the United States that science was behind, so all sorts of resources were put in and a number of jobs were expanded; they expanded fellowships and therefore the universities were expanded.”

How did it feel when you first returned to Czechoslovakia in 1961?

It felt very strange. At that time, I was at Brandeis University but I spent many summers at Stanford. At Stanford there was a very famous Czech mathematician, who should be better known, had made some really fundamental contributions. His name was Karel Loewner. He encouraged me very much to visit Prague because I always spoke Czech at home and I could speak it well and I was interested in Czech matters. So he wrote a letter introducing me to the maths faculty and they together with the Czechoslovak Academy of Science invited me to come. So I came in the summer of 1962 and since then I returned very frequently.

Was there anything that surprised you when you came here after the fall of communism?

“Things were already loosening up in the last years before the fall of communism. I remember that in the early days people were really afraid to talk. But in the last years, people somehow lost some of the fear of the government, I think especially in speech because so many people were insulting the government and making fun of their leaders. On the other hand, I did have one amusing experience that people were still afraid. One of the mathematicians had visited Cuba. He invited me to his apartment and he asked me to speak Spanish with him when we come to the courtyard because he didn’t want his neighbours to hear that he was hosting Americans.”

You were in touch with Czechoslovak science throughout much of the Communist era. How good was it?

I think it was very spotty. Certain things were extremely good – like certain kinds of chemistry. They invented here the optical contact lens, for instance, and other things of that sort. So certain parts were very good and the people who worked in science here were uniformly very talented and very good by and large. The trouble was that in mathematics, physics and many other fields, they had such a limited contact with the outside world; it was even difficult to have a contact with the Soviet Union. Also, one terrible thing was that the price of scientific journals and books in the West went up so steeply that by the time the 1970s came, they couldn’t afford them. But the education in science up to the first undergraduate years was still really excellent, I think. It was of course interrupted by the fact that many students were denied access to this education because of their political background. A lot of time was also wasted with courses about Marxism.