The outstanding mathematician Louis Nirenberg died January 26. I knew him from my own times at NYU, and I liked him very much. Nirenberg was a mensch.

But how exasperating to read the obituary in *Nature* describing him as “skating above emerging distinctions between pure and applied mathematics”. What nonsense! Nirenberg was the quintessential pure mathematician. He was no more an applied mathematician than Einstein was an electrical engineer.

This imperialist point of view is all too familiar, and it drives me crazy. Pure mathematicians like to think mathematics is one, and as some kind of a corollary, it follows that the great pure mathematicians encompass the applied side too. For a few, like von Neumann, this may be true. For most, it’s preposterous.

[5 March 2020]