here ...I'm not sure what to think because I don't exactly know what 1820 is a reference to.
If it is something analogous to there being no Marxists before - oh I don't know, 1848? - or no Keynesians before 1936 then it sounds like something I would agree with.
If it is something analogous to the claim that there were no classical economists before 1863 then I don't think it makes much sense.
UPDATE: Gene helps me out. The dating is apparently grounded in one guy's (John Henry Newman in this case) litmus test.
He also repeats the sedan chair/motor car metaphor he had in the main post. Look, we all agree that "I have legs and a T-Rex had legs so any history of Daniel Kuehn has to go back to the T-Rex" is stupid. "Keynes and Kalecki both talked about aggregate demand in similar ways, Kalecki somewhat before Keynes, so they are both 'Keynesian'." is plausible enough to talk about and indeed it has been talked about by a lot of people.
But if someone made the Daniel Kuehn/T-Rex analogy as a way of dismissing the induction of "proto-Keynesians" into the Keynesian camp they'd be rightly dismissed as silly.
A sedan car is not a motor car. It's missing... well... a motor. It belongs in a history of personal transportation of course. What Gene thinks this has to do with liberalism I'm not entirely sure.