SYNOPSIS: Reviews 'The Tipping Point.' Applauds the underlying idea but recognizes that it has little practical value.

More than 20 years ago I fell in love, as young social scientists will, with nonlinearity -- and in particular with the idea that large effects could have small causes. I was inspired by the economist Thomas Schelling's classic little 1978 book "Micro motives and macrobehavior," with its illustrative models of how seemingly trivial individual concerns (such as a mild desire to have some neighbors similar to yourself) could lead to extreme social outcomes (such as complete racial segregation). And I dreamed of a theory of everything -- of fashions and fads, booms and slumps, economic miracles and social catastrophes.

So when I read "The Tipping Point," the new best seller by Malcolm Gladwell, I sighed for my lost innocence. Mr. Gladwell is a very good writer, but he is also lucky: he has not yet been forced to confront the sad truth that it is far easier to tell nonlinear stories than to confirm them, let alone use them as a basis for action.

For those who haven't yet heard about it, "The Tipping Point" -- subtitled "How little things can make a big difference" -- has a pretty good chance of becoming one of those books that, arriving at just the right moment, reinforce a new public mood. After decades of disillusionment with social engineering, of backlash against the Great Society and all that, there is a new mood of social activism abroad in the land; and Mr. Gladwell offers hope that "tightly focused, targeted interventions" might work after all. So his book might be to the next decade what Michael Harrington's "The Other America" was to the 1960's.

Mr. Gladwell's main idea is an analogy between social movements and epidemics. With stories that range from the sudden resurgence of Hush Puppies as fashion footwear to the recent decline in New York's crime rate, he argues that behavior patterns, like viruses, can spread from a few individuals through a large population. (Oddly, he makes no mention of the biologist Richard Dawkins, whose analogy between "memes" -- infectious ideas -- and viruses had, I thought, itself spread widely even among the literati). And a small change in the environment, which makes a particular behavior pattern just a bit more likely to persist in one individual or be adopted by another, can sometimes cause sudden, large social change.

It's an idea that, in some broad and general sense, is certainly true. And if you have never thought about such things before, it can be mind-opening.

But a word of caution: If you accept Mr. Gladwell's conclusion that the analogy between epidemics and social change offers "a reaffirmation of the potential for change and the power of intelligent action," you are likely to be bitterly disappointed.

Why do I say this? Because when it comes to the idea that big events can have small causes, economists -- who ought to have a simpler problem, because they deal with the cruder emotions -- have been there and done that, repeatedly, for 60 years or more. And by and large the theories haven't worked.

For example, surely the spread of the Great Depression from Wall Street to the world at large was a sort of epidemic; more recently, the 1997-98 crisis in Asia was almost invariably described with terms like "financial contagion." Everyone who thinks about it seriously realizes that such crises must involve some kind of self-reinforcing process. But the ingenious "nonlinear business cycle theory" that briefly flourished in the 1940's turned out to be no help in predicting or preventing future recessions. I have a personal stake in believing that the currency crisis models some of us devised in the midst of Asia's turmoil will have a better fate; but history is not on my side.

Another example: Economists once thought that a brief "big push," perhaps concentrated on a few key sectors, could jump-start a stagnant economy into rapid modernization. But none of the deliberate efforts to engineer an economic takeoff delivered on their promise; when economic miracles like Korea's sudden surge in the 1960's (or our own recent productivity revolution) occurred, they have always come as a surprise.

I'm not saying that "focused, targeted interventions" aren't worth trying. But don't count on much success. Little things can indeed make a big difference; but they're usually not the things you were watching, or the difference you expected.

Originally published in The New York Times, 4.12.00