By James Randi

Scribners. 256 pp. $19.95

Most people accept the possibility of prophecy, just as they believe (without thinking about it in any analytic way) in the efficaciousness of wishes passionately held, in poetic justice, in precognition and psychic insight. We live most of our lives in an unconsidered prerationality, and find no difficulty with it. Difficulties arise only when a systematic mind takes up such beliefs, and meets another systematic mind bent on dismantling them.

Michel de Nostredame was an astrologer and almanac maker of the 16th century, who used a Latinized form of his name, as scholars of his time often did: Nostradamus. In addition to the usual predictions accompanying his almanacs, Nostradamus compiled a lengthy series of quatrains, crabbed and obscure -- automatic writing, almost -- that were claimed to be prophetic of events that would take place years, even centuries on. For reasons that even James Randi fails to make clear, this collection of prophecies -- and not similar ones generated in that century or earlier centuries -- has persisted, has gained rather than lost authority, and is proverbial now as a Book of Knowledge in which the wise can descry the shape of the future.

The squaring off of Nostradamus and his believers with Randi is a wonderful idea. Randi is of course "The Amazing Randi," skilled stage magician and master of illusion, who like Houdini before him has devoted a large part of his career to unmasking those who use the techniques of stage magic to pretend to supranormal powers. He was the nemesis of Uri Geller (Randi could bend spoons too, and told how Geller did it) and recipient for his educational efforts of a MacArthur Foundation "genius grant," the choice of Randi being a bit of genius in itself.

How does he match up against the old mage? It ought to be said that Randi's opponents are really the later interpreters and not Nostradamus himself, toward whom he takes a patronizing but not ferocious attitude: This distinction may account for the otherwise obscure title of his book. It ought also to be said that Randi is not really a scholar of 16th-century intellectual trends, or anywhere near as able at manipulating historical tools and materials as he is in manipulating scarves, swords and rabbits.

"Though we may look to the Renaissance for poetry and music," he writes, setting the background for Nostradamus, "not much really brave, hard thought took place." Now it is possible to suppose that the thought of Calvin, Machiavelli, Erasmus and Paolo Sarpi concerned itself with matters no longer considered central -- with God, or with how a Christian society should work, how princes should behave, what constitutes justice -- but that certainly does not make it less brave or less hard. Randi seems to believe that at any age and at any time, the wheat is easily separated from the chaff, the hard bright truths from the stuff and nonsense, and is unforgiving of past thinkers who mixed the two: They ought somehow to have known better.

In addition to his wooden lack of sympathy with past intellectual endeavor, Randi is given to odd unscholarly procedures (he cites an 1848 edition of the Encyclopedia Britannica as an authority, for instance). He has assembled rather than constructed his book, in a random cut-and-paste fashion that strikes a reader as rather medieval, though I suspect the word processor is responsible. He makes room in it for multiple diversions and digressions, a disquisition on Hermes Trismegistus, a life of the English astrologer John Dee that is full of small errors.

None of this would matter much if it didn't occupy so much of a short book. For when Randi settles down to demolishing the Nostradamians, he comes brilliantly into his own. Nostradamus is supposed by his latter-day flacks to have predicted the French Revolution, Napoleon and Hitler's rise, among other things, and Randi takes up several of the key quatrains on which believers have relied. He not only makes effective fun of their hopelessly inadequate methods of analysis, but makes some striking analyses of his own of what Nostradamus might have actually been thinking about. Here Randi genuinely engages with the past to solve the mysteries of a difficult text, rooting the quatrains convincingly in a geography of Michel de Nostredame's youth and the events of his day.

There should have been more of this kind of work in the book. I suspect that the reason there is not is that Nostradamus actually turns out to be quick work to demolish. The constructions of his later promoters vanish into (hot) air as soon as they are looked at closely. Like the tonic bottles of the medicine showman, the prophecies of Nostradamus are but the center of a rhetorical invention, and uninteresting in themselves.

Well, we might have known. But then again -- though Randi and his fellow hardheads gnash their teeth -- the unmasking of one or a dozen instances of false prophecy will not keep most of us from pondering others, or noting occult urgings or prophetic dreams, usually to forget them again when they yield no result. The committed battlers over prophecy and the occult -- those who believe such things are Really True and those who can prove they're Really Not True -- are the minority, locking horns while the rest of us watch with amusement.

The reviewer's novel "Little, Big" will be reissued this fall.