The trouble with the history of ideas is that it is endless. This is all very well for the scholar, but fatal for the sort of jeu d'esprit attempted here. It is Professor Gay's fancy that the shades of Voltaire and Erasmus, with Lucian as master of ceremonies, are debating the effects of the Enlightenment ""on history and hope, imagination and reason, constraint and freedom--and on its meaning for our time."" These dialogues, more Shavian than Platonic, therefore putatively entertaining as well as thought-provoking, soon flounder, however, in schematic shallows. They resemble a seminar transmitted on an educational network, the participants never coming to a particular point, finally concluding through sheer exhaustion. Gay's hero, Voltaire, comes across badly, a complacent know-it-all. When Erasmus says, ""I wrote to purify my faith; you borrowed my words to destroy it,"" Voltaire replies, ""The only way to purify your religion was to destroy it."" True, Voltaire is always speaking in the name of tolerance and the free use of the critical faculties, but he seems tiresomely oppressive, especially when Gay has him pontificating on post-Enlightenment events: ""The logical positivists carried the torch of analysis into dark corners and showed that the most profound mysteries of metaphysics were nothing more than cobwebs of the mind."" That, surely, would never pass muster in a philosophy course. Gay, a brilliant historian, is much better read ""straight,"" as in his celebrated studies. If one wants to be ""deep"" one must also be ""playful,"" said Shaw, or one loses one's audience.