In the ’40s mathematics moved from its traditional way of presenting results to a highly abstract approach favored by Bourbaki, this group of French purists. And it became forbidden to explain in a mathematics article what you were going to do; or what you had done when you finished; to give any motivation; to give any non-trivial examples even. You could give a trivial example in a line or two, but you were not allowed to give, to explore a non-trivial examples. And as a result mathematics and science, particularly physics, drifted apart where previously they'd had a lot of mutual stimulation. It was very sad and I'm glad that later on the trend moved in the opposite direction to some extent.

In any case, I was quite impressed with… with the Yang-Mills theory although I didn't see how in its precise form it was applicable to anything. An exact gauge invariant theory with the group SU(2), and I didn't know what that would apply to. But I assumed that it would be very important some day in some connection, especially if we could develop a soft mechanism for breaking its symmetry; but I didn't see how to do that at the time. I didn't… I don't imagine that in ’55 I was already thinking about how, in a Yang-Mills world, knowing about symmetries would tell you almost immediately about dynamics. That's something I understood only much later, but it's certainly true.