Most people spend the greater part of their working lives carrying out more or less the same activity but from time to time face the inconvenience of changing jobs. I’ve had the opposite experience. As I write this essay, I am beginning my fortieth year in the same job: economics professor at Harvard. But from time to time I’ve shifted the focus of my work to such an extent that the new path feels, in many ways, like a new career – not just different questions to consider but different starting presumptions, a different set of relevant institutions, different background literature, and a different cast of characters whose contributions and judgment matter.

To be sure, all this is a matter of perspective. To some – perhaps to most people not engaged in an academic or research enterprise – what has seemed to me like a series of career changes may well appear far more seamless. After all, I’ve continued throughout to write books and articles about economics and to teach economics to both graduate students and undergraduates at my university. Isn’t that all really the same thing? From my perspective, no it isn’t. To me, these transitions increasingly have had the feeling of career changes. To the question of what it’s like to have “done the same thing” for so many years, my reaction is that I wouldn’t know; I haven’t.