A Reminiscence of
Thomas Kuhn
Jed Z. Buchwald
California Institute of Technology
In the fall of 1967 I entered Princeton as a Freshman intending to major
in physics but interested as well in history. The catalog listed a course on
the history of science, taught by a Professor Thomas Kuhn with the assis-
tance of Michael Mahoney that seemed nicely to ªt both interests. The
course proved to be peculiarly intense for something about what was, after
all, obsolete science as, each week, hundreds of pages of arcana from the
distant past had to be absorbed. Professor Kuhn would pace back and
forth in lecture, smoking intensely and talking rapidly to an elaborate
outline drawn on the board at the beginning of each class. In tutorial,
Mahoney (who passed away in 2009) developed Kuhn’s points, forcing
students to grapple with the meaning and signiªcance of the many com-
plicated texts that were assigned. That summer I worked as Mahoney’s re-
search assistant and, subsequently, as Kuhn’s also.
Though the Structure of Scientiªc Revolutions was assigned in that class,
Kuhn never put much explicit emphasis on it; he lectured almost entirely
about the historical materials we were reading. Nevertheless it was clear
that he had a guiding vision about science. Everything he spoke about,
from Ptolemaic eccentrics to stationary orbits in the Bohr atom, seemed to
exemplify a way of thinking about science that was certainly unusual
for the time. It seemed that he was continually trying to excavate a struc-
ture beneath the dead science’s apparent surface, something that could
provide a key to understanding how it worked. He would often empha-
size precisely what seemed to be the oddest, or the most irrelevant, pas-
sage or point in the reading. Kuhn never, or rarely, spoke explicitly about
paradigms, normal science or incommensurability, but every story he told
had things very much like those three elements at its core. Yet they took
Perspectives on Science 2010, vol. 18, no. 3
©2010 by The Massachusetts Institute of Technology
279
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280
A Reminiscence of Thomas Kuhn
their shape and meaning not through explicit deªnition but rather
through the examples that he developed, and through the ways he an-
swered questions.
During my time as Kuhn’s research assistant we would meet every
week or two to talk about old physics. He would always emphasize the
need to uncover what kinds of characteristic problems were at issue in the
past, and about how these problems connected to mathematical and theo-
retical structures, though not much at the time about experiments proper.
In the spring of 1972, Kuhn taught a graduate seminar on the history of
thermodynamics. The readings—all of them primary sources—had been
carefully prepared and put on reserve. Each week one of the students was
responsible for taking the class through the texts. Kuhn did not want a
simple summary of relevant issues. He expected you to have ªgured out
precisely what made the text tick. He already had pretty strong notions
about the materials, and if you came up with something different from
what he had in mind then you had to argue for it line by line, sometimes
equation by equation (since most of the texts dealt with in that course
were strongly mathematical).
Kuhn’s most detailed effort to work through a body of past physics—
his Black-body Theory and the Quantum Discontinuity—appeared in 1978.
He had been hard at work on it since 1971. To those who knew him well
over the years, the book itself very nicely exempliªes Kuhn’s special ap-
proach to the history of science as well as his particular views about
scientiªc development. Like most things that he wrote, Black-body Theory
generated controversy, some directed at its apparent failure to apply what
he had himself laid out in Structure, some directed at his speciªc, technical
claims. It seemed to many of us who knew him that Kuhn was not both-
ered much or even at all by the former critique, but he was very much con-
cerned with technical criticisms. His need, even compulsion, to ªnd the—
not a—core of meaning that unites a disparate series of texts, to extract
that largely-implicit structure and to display how it governed and con-
nected to a set of canonical problems, powerfully directed his histori-
cal research. Technical criticism accordingly bothered him a great deal,
precisely because it went to the core of what Kuhn took to be his cen-
tral historical task, which was to uncover the hidden integrity of past
science.
As the years went by Kuhn increasingly found historical research to be
difªcult. There seem to have been two reasons for his growing reluctance
to read or to do history. He had trouble absorbing secondary work, in ma-
jor part because he brought to histories the same intense commitment to
the text’s meaning that he brought to source materials. Vagueness both-
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Perspectives on Science
281
ered him no end, as did failure to produce the sort of analysis that he
found most useful and interesting. But Kuhn was also not himself in-
clined to grapple with archival materials; he focused almost all of his own
historical work on printed works. Yet, and he knew this to be so, the very
structures that he so strongly wanted to uncover could often only be exca-
vated from unprinted materials.
Kuhn’s move to the Department of Philosophy at MIT in 1979 exemp-
liªes his own sense that the issues with which he was most directly con-
cerned were philosophical in nature, though he remained deeply commit-
ted to careful historical understanding, as he conceived it. In 1986 he
wrote me a letter that contained the following remark: “I think of my pri-
mary talent as a hard-earned ability to read a text, ªnd a way to make it
make sense by discovering the conceptual structure that lies behind it. It’s
the experience of ªnding hidden structures that underlies The Structure of
Scientiªc Revolutions and that I’m now back trying to analyse again.” Those
of us who studied under him, and many who knew him over the years,
will recognize here his distinctive voice and point of view. Voice and view
demanded and conveyed an uncompromising, rigorous attempt to push
beneath the surface of technical work, to ªnd out how it worked.
In 2001 I became director of the Dibner Institute for the History of
Science and Technology at MIT, where each week a Fellow would give a
talk. Tom attended many of these, and once a month or so we would have
lunch together. During these last years of his life he was trying hard to
develop a lexical understanding of what it is about scientiªc work that
produces difªculties of mutual comprehension between proponents of dif-
ferent systems that ostensibly cover the same phenomenal range. The
problem, that is, of incommensurability. Many of our talks ranged over
examples of that sort of thing, taken not however from such wide-ranging
schemes as Ptolemaic versus Copernican astronomy, but from much more
limited structures, such as the arguments between proponents of an optics
based on waves and those who thought in terms of rays. Or between Brit-
ish developers of electromagnetic ªelds and their German counterparts.
Tom’s new understanding orbited about his conviction that the deepest
differences between scientiªc schemes concern the ways in which they re-
spectively divide their universes into kinds of entities. Incommensurabil-
ity, he thought, was not a vague difference in views, but a speciªc viola-
tion by the one scheme of another’s afªliation among kinds—a violation of
the principle that a given kind can be an immediate subset of at most one
other. That, it seemed to him, was a general property of scientiªc systems
which captures differences among them.
We spoke about this many times, which led me at his urging to write a
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282
A Reminiscence of Thomas Kuhn
paper applying the idea to the history of wave optics.1 We talked about
how to do this as the paper took shape, and the diagram that it included
resulted directly from our discussions. The dark lines represent the kinds
of polarized and unpolarized light that were deployed by those who
thought of light in terms of rays in the early 1800s, satisfying the one-
immediate-ancestor criterion. The dotted lines show instead how practi-
tioners of wave optics grouped kinds of light together in ways that vio-
lated the groupings of ray practitioners. These differences had instrumen-
tal consequences that appear quite directly in the literature of the period.
In our discussions Tom was interested for the most part in the categorical
groupings, less so in their connections to measurement processes, though
he did tell me that he intended to think through the latter in more detail
in relation to kinds. He never really did ªnd the time to do so.
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A tree of kinds for polarized light, developed by Buchwald during discussions
with Tom Kuhn in the early 1990s.
I continue to think that Tom was substantially correct about the im-
portance of incommensurability in scientiªc practice, and that the concept
is best conceived in terms of a tree structure for kinds. Certainly his way of
understanding cannot easily encompass the sort of thing that takes place
when, say, someone trained as a physicist moves into biology, giving rise
perhaps to new regimes with concomitant developments in social, cultural
1. “Kinds and the Wave Theory of Light.” Studies in the History and Philosophy of Science,
23:39–74.
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Perspectives on Science
283
and institutional structures. Though Tom would occasionally talk about
such things, he really had very little to say about them in later years since
they do not map simply onto issues of incommensurability in the way that
he had come to think about the latter. That notion occupied him to the
end of his life and, he often told me, constituted his most important con-
tribution to understanding the character of scientiªc work.
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Taken by Buchwald at Tom and Jehane Kuhn’s home on Memorial Drive in Cam-
bridge in the spring of 1991.
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