He's ODed on coffee, I think:
2006 06: Neuropharmacological Foundations of the Public Sphere: The importance of coffee-houses in the Enlightenment, and the rise of the public sphere, is a historical common-place. But it's also puzzling: historians can say a lot of sensible things about how, as a social setting, the cafe was conducive to the give and take of (more or less) rational argument, and (relative) indifference to social standing in favor of persuasion. But I've never heard a good story for why coffee houses had to be run that way, nor that (say) taverns weren't, or couldn't have been, run that way. So, while not denigrating the social factor, it doesn't seem to explain why this connection took hold. Now, at last, scientific proof that Enlightenment had a sound material basis (via Mind Hacks):
Pearl Y. Martin, Jenny Laing, Robin Martin, and Melanie Mitchell, "Caffeine, Cognition, and Persuasion: Evidence for Caffeine Increasing the Systematic Processing of Persuasive Messages", Journal of Applied Social Psychology 35 (2005): 160-18: Abstract: Caffeine is known to increase arousal, attention, and information processing--all factors implicated in facilitating persuasion. In a standard attitude-change paradigm, participants consumed an orange-juice drink that either contained caffeine (3.5 mg/kg body weight) or did not (placebo) prior to reading a counterattitudinal communication (anti-voluntary euthanasia). Participants then completed a thought-listing task and a number of attitude scales. The first experiment showed that those who consumed caffeine showed greater agreement with the communication (direct attitude: voluntary euthanasia) and on an issue related to, but not contained in, the communication (indirect attitude: abortion). The order in which direct and indirect attitudes were measured did not affect the results. A second experiment manipulated the quality of the arguments in the message (strong vs. weak) to determine whether systematic processing had occurred. There was evidence that systematic processing occurred in both drink conditions, but was greater for those who had consumed caffeine. In both experiments, the amount of message-congruent thinking mediated persuasion. These results show that caffeine can increase the extent to which people systematically process and are influenced by a persuasive communication.
I should perhaps add that the leap from their findings to the rise of modern rationalism is entirely my own.