Otium, in ancient Roman time, was the time productively spent pursuing the agenda of your personal growth – be it the cultivation of your garden or the virtuous studium of arts & science. This concept was clearly coming from the greek “paideia”: in XIX century’s Germany it will be given a new incarnation in Wilhelm Von Humboldt’s foundation of the modern University.
It is easily forgotten that, when one attends a research seminar, one is simply following on the footsteps of that venerable tradition.
A good metric for the rationality of a social system could in principle be based on what is the ratio of aggregate time spent by the economic agents in jobs perceived as conducive to personal growth as opposed to jobs perceived as mere toil.
The (social) target function to minimize would then involve not the time spent on the job market, but the toil itself, something Keynes was hinting at in his famous piece on the “Economic Possibilities for our Grandchildren” (1930).
Clearly a necessary condition for that is again and again that technology reaches a stage where all the toil is left to automata. The Human Use of Human Beings is just that.