We are all familiar with ideas said to be ahead of their time, Babbage's analytical engine and da Vinci's helicopter are classic examples. We are also familiar with ideas "of their time," ideas that were "in the air" and thus were often simultaneously discovered such as the telephone, calculus, evolution, and color photography. What is less commented on is the third possibility, ideas that could have been discovered much earlier but which were not, ideas behind their time.

Experimental economics was an idea behind its time. Experimental economics could have been invented by Adam Smith, it could have been invented by Ricardo or Marshall or Samuelson but it wasn't. Experimental economics didn't takeoff until the 1960s when Vernon Smith picked it up and ran with it (Vernon was not the first experimental economist but he was early).

(Economics, and perhaps social science in general, seems behind its time compared say with political science.)

A lot of the papers in say experimental social psychology published today could have been written a thousand years ago so psychology is behind its time. More generally, random clinical trials are way behind their time. An alternative history in which Aristotle or one of his students extolled the virtue of randomization and testing does not seem impossible and yet it would have changed the world.

Technology can also be behind its time. View morphing ("bullet time") could have been used much more frequently well before The Matrix in 1999 (you simply need multiple cameras from different angles triggered at the same time and then inserted into a film) but despite some historical precedents the innovation didn't happen.

Ideas behind their time may be harder to discover than other ideas–"if this is so great why hasn't it been done before"? is an attack on ideas behind their time that other innovations do not have to meet. Is this why social innovations are often behind their time?

What other ideas were behind their time? Are some types of ideas more likely to be behind their time than others? Why?