So I started arguing with him about this inherent contradiction: being an historian of science and at the same time preaching a doctrine that made history of science impossible. And it got nasty, it got really nasty. […] And then he threw the ashtray. And he missed. I always wanted to film a reenactment…

☛ “The Ashtray” a lecture by Errol Morris for the Princeton University Public Lectures Series, November 15, 2010, 00:24:24. Listen to Morris’ lecture or watch the video on the Princeton Univeristy Podcasts page. Optionally, access the podcast via iTunes (free).

Errol Morris studied with Thomas Kuhn at Princeton in the early 70’s. Morris didn’t like the idea of “incommensurability” and got into a “nasty” argument about it with Kuhn who apparently threw an ashtray at him.
In his lecture Morris explains to the audience why he thinks incommensurability is a problem, especially for the historian of science: “If you’re in paradigm A, you really can’t understand what people are doing in paradigm B because the two are incommensurable with each other.” According to Morris, an historian of science living today couldn’t understand past sciences, since they belong to different paradigms. Therefore the “inherent contradiction” for Thomas Kuhn, an historian of science, in coming up with this idea of incommensurability.
However, in a famous (and much debated) postscript Kuhn wrote in 1969 for the second edition of The Structure of Scientific Revolutions, one can read the following explanation:

Briefly put, what the participants in a communication breakdown can do is recognize each other as members of different language communities and then become translators. Taking the differences between their own intra- and inter-group discourse as itself a subject for study, they can first attempt to discover the terms and locutions that, used unproblematically within each community, are nevertheless foci of trouble for inter-group discussions.  (Locutions that present no such difficulties may be homophonically translated.)  Having isolated such areas of difficulty in scientific communication, they can next resort to their shared everyday vocabularies in an effort further to elucidate their troubles.  Each may, that is, try to discover what the other would see and say when presented with a stimulus to which his own verbal response would be different.  If they can sufficiently refrain from explaining anomalous behavior as the consequence of mere error or madness, they may in time become very good predictors of each other’s behavior.  Each will have learned to translate the other’s theory and its consequences into his own language and simultaneously to describe in his language the world to which that theory applies.  That is what the historian of science regularly does (or should) when dealing with out-of-date scientific theories. (Thomas S. Kuhn, The Structure of Scientific Revolutions, “Postscript – 1969”, Third Edition, University of Chicago Press, Chicago, [1962, 1970] 1996 / available online)

Errol Morris goes on to explain that he views the concept of incommensurability as a “deeply postmodern idea”. He provides his audience with a definition of the word “postmodern”: “By ‘postmodern’ what do I mean? When I think of postmodernism I think of people who want to deny truth: there is no such thing as absolute truth. There’s relative truth, subjective truth… Or like my friend Werner Herzog would call it ‘ecstatic truth’… I have my own way of describing ‘ecstatic truth’: I call it ‘lying’. ”
Errol Morris is a virulent critic of what he calls “postmodernism” and “relativism”. He believes there are truths in the world worth being investigated. He often quotes his documentary The Thin Blue Line (1988) as an example. Either you killed a man or you didn’t: “There is nothing post-modern about the electric chair.”, he once said during a lecture he gave at the Berkeley Graduate School of Journalism. One can also read a short essay he wrote back in 2005 for NPR’s “I Believe” program titled “There Is Such a Thing as Truth”.
As much as I think I understand what he means and share the reasons why he believes in those ideas, I would very much like to see Errol Morris take the time to explain his views in more details, with the same rigor and meticulosity he used, for example, in the very intelligent essays he wrote for The New York Times. I can’t help myself but to think that his views on “postmodernism” and “relativism” are a little too much simplistic in the ways he presented them until now. For example, there’s also an “inherent contradiction” to the idea that “there is no such thing as absolute truth”: if it is true, then it is not. The same goes for “Everything is relative” (a statement that should be, by its own rule, relative). Such contradictions make for quite weak opponents, whereas I’m sure Errol Morris is thinking of much more worthy adversaries when he takes on “postmodernism” and “relativism”.
Now, there isn’t much more about all this in the Princeton lecture quoted above. However, a couple of days ago Errol Morris announced on his Twitter account that he was working on an essay about incommensurability and that it was about to be published (most likely in The New York Times where he has a blog): “It will go online in early February”. I’m looking forward to read it. Meanwhile I’ll read again some of his other essays: one can find most of them listed in the Archive section of Errol Morris’ official website.
For more on the idea of “incommensurability” see the corresponding entry in the Standford Encycloedia of Philosophy.

I discussed the Pythagorean legend surrounding incommensurability in a short essay: On the threshold of knowledge: Pythagoreans, incommensurability and the experience of modernity.