Defining the New Sexuality : VICE VERSA: Bisexuality and the Eroticism of Everyday Life, <i> By Marjorie Garber (Simon & Schuster: $30; 528 pp.)</i>

This is the land of either-or, Republican or Democrat, male or female, black or white, right or wrong, Coke or Pepsi, straight or gay. A choice not based on duality--in fact, a reality not based on duality, such as bisexuality--will fry some already overloaded brain circuits.

“Bisexuality marks the spot where all our questions about eroticism, repression and social arrangements come to crisis.” In “Vice Versa,” Marjorie Garber elaborates on this crisis for 528 pages, plus 56 pages of notes.

Crisis for whom?

First, of course, are those legions of Family Valuers for whom sex and Satan appear interchangeable unless of the most tepid variety. For some lesbians and gay men, in turn, bisexuality gets their knickers in a twist. For many heterosexuals, bisexuality is just too confusing.

For other people, the bisexual represents the ancient bugaboo, the non-monogamous person. Why this gets pinned on bisexuals is a curiosity. “Until death do us part” was easy to keep when the average life span was about 24 years, which it was when the Old Testament gave us our narrow definition of marriage. The bisexual is accused of having his/her cake and eating it, too.

For all the finger-pointing, name-calling and ludicrous efforts at categorization, what is a bisexual? The great strength of “Vice Versa” is that Garber doesn’t tell you--exactly. Bisexuality is comprehensively explored but never pinned down. For example: “Bisexuality means that your sexual identity may not be fixed in the womb or at age two, or five. Bisexuality means you may not know all about yourself at any given time.” Those are words guaranteed to freeze the blood of the guys who smoke Joe Camels.

Marjorie Garber, an English professor at Harvard and author most recently of “Vested Interests: Cross Dressing and Cultural Anxiety,” has written a book that is academic in tone, with occasional personal references. She posits three mythological types of bisexuality, “as experience (Tiresias), as essence (Hermaphroditus), and as desire (Aristophanes’ fable in Plato’s ‘Symposium’).”

Tiresias spent part of his life as a man, part of his life as a woman and then back as a man once more. Hermaphroditus sported the genitals and attributes of both sexes. Whereas in the “Symposium,” Aristophanes, the greatest of the Attic comic playwrights, says once upon a time humans were big, round powerful creatures. We were men-men, women-women and men-women with four legs and arms. We challenged the gods, which put their celestial noses out of joint, so Zeus split us in half. Ever since, each human has sought his/her other half.

While this proves the ancient Greeks knew a good thing when they saw it, it offers no relief to the straight-jacketed modern mind of the West.

For the less than thoughtful person, bisexuality has devolved to a sexual condition wherein a person can enjoy sexual and perhaps emotional intimacies with both genders. This definition, on the surface, puts everyone in their place. It is identity based on action so people can forgo the vapors: They aren’t bisexual. However, if identity encompasses feelings, better break out the smelling salts. Most of us have loved someone of our own sex. We’re told it’s OK if sexual desire is absent. Think of it as sanitized love.

Ah, if only desire were that simple.

The fundamental irrationality of desire is the true affront to our times. So, like everything else in America, we focus on the symptom not the cause. The symptom is unbridled sexuality, the practice is bisexuality.

“Vice Versa” examines such diverse people as the late Paul Monette, Eleanor Roosevelt, Robert Graves, Shakespeare, Emma Goldman, the Stracheys (they were hilariously various), Paul Bowles, Virginia and Vita (again) and many others who may or may not identify themselves as bisexual despite their involvements with men and women. For those who later married, they often brushed off the same-sex affair. For others, sleeping with the opposite sex was a milepost on the road to a true and righteous gay identity. A few seemed to take it all in stride without the need to qualify sex or its more mysterious big sister, love.

Someone who couldn’t take anything in stride was that poor physician from Vienna. One hopes Sigmund Freud knew some peace in life--surely there is none in death as he is picked over constantly. Bisexuality fascinated him and ultimately caused a blow-up with one of his friends. For all his faults, Freud remains interesting.

Carl Jung, on the other hand, is exposed for the very silly man he was. Garber demolishes him, with arid delight, as he circles bisexuality, androgyny and confident women (read in: lesbians, those naughty girls). Garber writes: “Despite Jung’s insistent idealization of archetypal androgyny in myths and legends, the phenomenon of ‘feminine’ men and ‘masculine’ women in real life clearly throws him off-balance. To be self-assured with men is enough, apparently, to destroy ‘feminine charm.’ It is all too clear here exactly who is disconcerted and who is left stone-cold.”

Apart from ripping Jung stem to stern, “Vice Versa” demonstrates the agonized foolishness that attends the drama of bisexuality. In all those 584 pages few people emerge with anything resembling common sense, much less a sense of humor. One such person was the poet Edna St. Vincent Millay and the anecdote is worth repeating. “ . . . when cornered in the twenties by a poem-writing psychoanalyst inquiring into the source of her constant headaches [he asked] Did Millay think she might have, even subconsciously, an ‘occasional erotic impulse’ toward someone of her own sex? ‘Oh, you mean I’m homosexual!’ replied Millay equably. ‘Of course I am, and heterosexual, too, but what’s that got to do with my headache?’ ”

Indeed.

In that spirit, I am reminded of a line I wrote in 1968 when challenged on the subject by some in the nascent feminist movement: At least I’ve doubled my chances of a date on Saturday night. And that’s what’s missing not just from “Vice Versa” but in these stale times: that rollicking sense of fun, part of which is multi-sexual.

Given the fervent Puritanical temper of the times, Marjorie Garber has written with great intelligence about bisexuality and she should probably get out of Dodge as fast as possible.