At What Age Do Philosophers Do Their Most Influential Work?

In an earlier post, based on an unsystematic sample, I estimated age 38. Today, with a broader and more systematically collected sample, I'm retracting that. Mostly.

Here's what I did:

First, I created a massive super-bibliography consisting of all the bibliographies from non-historical entries in the Stanford Encyclopedia of Philosophy. I then examined the SEP citation patterns of all philosophers born from 1550 to 1919 who were cited in at least nine distinct entries -- 53 highly influential philosophers in total.

Next, I noted which of these authors' works were the most cited in the SEP (an imperfect measure of influence, of course, but it avoids my having to rely on my own even more imperfect judgment); and I estimated the age at which that work was produced as publication date minus birth year minus 2. (Minus two because the average person spends half of the year at which she turns age X at age X-1 and because of the typical delay between writing and appearance in print.)

(A few more methodological details: Wittgenstein's Investigations, published posthumously, I estimated as produced at about age 55, based on historical evidence. In the case of multi-edition or multi-volume work, I considered the first-published work. In the case of a tie in number of citations (which happened twice) I took the midpoint as my estimate. Two authors I excluded because they had no single work cited more than three times in front-page, non-historical SEP bibliographies: Peirce and Dewey. And because the question concerned relative productivity over the life span I excluded five authors who died before age sixty: Descartes, Nietzsche, Austin, Ramsey, and Prior.)

Here, then is the final list, arranged by age:

[If Reid isn't displaying correctly, another version of the chart is here.]

The mean estimated age of this group is 44. The mean age remains 44 if I tweak the measure by adding in any works cited at least half as often as the most-cited work and then take the midpoint of the resulting age range. I would guess that 44 is probably a smidgen on the old side as an estimate of the age at which philosophers' most influential work is done, since most work brews for several years before finally appearing in print. In that sense, the 38-year-old estimate isn't perhaps too far off.

But to my eye the more striking fact about the chart is this: How straight the line is from the mid-20s to the early 60s. If this were a bell-shaped distribution around 44, we should see flatter slopes at the beginning and the end -- as we do in fact see starting in the mid-60s. The straightness of the line suggests that there's isn't so much a peak age at which the most elite work in philosophy has been done but instead a long plateau from the mid-20s into the 60s, then tapering off.

There are various potential explanations for the tapering off that seems to start in the mid-60s; I wouldn't rush to the conclusion that the tapering reflects cognitive decline. Other possibilities include decline in health and the prioritizing of other goals.