FOR THOUSANDS OF years, people have wondered about the reasons behind suicide. Many theories have been put forward. No one, however, has found a complete or satisfactory answer.

Each case of suicide is separate and individual, with its own complications, sorrows, and mysteries. There is no single explanation for what causes people to kill themselves. Writer George Howe Colt put it this way: "Trying to find the answer is like trying to pinpoint what causes us to fall in love or what causes war." And the distinguished psychoanalyst Karl Menninger, who spent much of his life studying suicide, once remarked, "It's a durn mystery, you know, in spite of all we've written about it."

Still, some progress has been made in understanding the roots and immediate causes of this disturbing social phenomenon. The ongoing research into the question...