“Rest, with nothing else, results in rust,” Wilder Penfield wrote in his great essay The Second Career: “It corrodes the mechanisms of the brain.”

The essay was an argument against the idea that retirement should be a period of idleness (unless by idleness you meant “activity without effort,” as he put it in another essay), but instead should be a phase in which we find and develop a second career.

In a way it is true of every man— or it should be true— that his second career begins as soon as he embarks on the primary that will yield him a livelihood. Whatever he does as a citizen or parent is part of the second career, and the two run concurrently until perhaps the second outlasts the first….

In fact, Penfield’s own favorite teachers, Charles Sherrington and William Osler, both had second careers as authors and bibliophiles: Sherrington published a book of poetry decades after studying poetry in college, while Osler became noted as a medical historian and antiquarian.

The time of retirement should be reorganized and renamed. It is the time for embarking on a new career, the last career perhaps, but not necessarily a less enjoyable one; not, perhaps, a less useful one to society. Disease and disability may overtake men at any age, of course, and force them to withdraw from work. But the capacity of the human brain for certain purposes often increases right through the years that are marked for standard retirement. And who can say? Those purposes may be what the world today needs most.

One of the best things about working on Rest has been the discovery of so many people who defy our common assumptions that young people are just smarter than everyone else, and that by the time you’re 30 (or maybe 40 or 50) all you have to look forward to is the slow decline of your faculties, followed ultimately Death’s clammy embrace and the sweet release of oblivion.

Penfield and almost everyone else I’m writing about would have said, screw that. They’re models for us all.