“I have been all my life an extremely promiscuous friend,” Joseph Epstein said Tuesday at Barnes & Noble Upper East Side, discussing his new book, “Friendship: An Exposé” (Houghton Mifflin).

He recalled having chosen to become a popular boy in high school, and cultivating a vast number of friends. He cited Plutarch, who felt that a man or a woman should not have more than seven. Looking back over the decades, Mr. Epstein said he had made about 75 to 80 friends. “How did I get so many?” He said perhaps it was because he lived in the city that he grew up in and kept friends from early years, or because as a university teacher, he had become friends with about 25 former students over years of teaching.

Mr. Epstein quoted the expatriate philosopher George Santayana, who once noted that a best friend is a person with whom one “can be most human.” But Mr. Epstein said he would not be dwelling on the delights of friendship, which he hoped all had experienced. “Let’s instead get to the subtitle of the book — an exposé. What exactly am I exposing in this book?” He answered that he was exposing the Hallmark greetingcard view of the subject, which, he said, tends to go something like this:

To a very special person
You’re caring and sharing
And always there for me.

But Mr. Epstein puckishly added, I’ve invented my own Hallmark card,” not on the market, which went like this: We’ve been friends for so long– Why don’t we stop?

A former editor of the quarterly magazine the American Scholar, Mr. Epstein said maybe the “Hallmark view of friendship” prevailed nowadays because there largely is an absence of strong contemporary writing on the subject of friendship. He expressed disappointment that much of what had been written recently was of “the how-to kind”: how to make more friends, how to survive broken friendships, and so forth. “It’s all vaguely therapeutic and written by authors whose names end in the initials Ph.D.”

He said friendship might be too complex and nuanced to be captured by a single theory. Freud’s view, that all friendship was essentially erotic, was a disaster, he said. (In an aside, Mr.Epstein quipped that he had come to believe that Freudian psychoanalysts, like Germany after the war, ought to be made to pay reparations to their patients.)

Mr. Epstein opposed what he described as a contemporary tendency of people to rely on friends as surrogate therapists. He recalled someone saying, “A true friend is someone you can call at 3 a.m. and tell all your troubles to. “I say yes,” Mr. Epstein added in deadpan, “but only once.”

Some aspects of friendship had changed, he averred. Women and men could now meet in non-sexual friendship in a way they could not in his father’s generation. And through email, chat rooms, and technology, “techno friends” could be friendly without requiring personal presence.

Mr. Epstein also said the definition of friendship alters as one grows older. He said the great time of friendship is probably adolescence, when life is full of passion and there is little else to interfere. But he said he now merely expects a friend to have a set of reasonably correct assumptions about the kind of person his friend is: to know something about how the other’s mind works, how his tastes run, what he finds amusing or intolerable.

Mr. Epstein set out a few general notions on the subject: First, one must never try to change friends. He described how the sociologist Edward Shils was always trying to reform the novelist Saul Bellow. He really wanted Bellow to be Thomas Mann with Jewish jokes on the side, Mr. Epstein said.

Also, one must not expect unanimity of opinions among friends on every issue, e.g. the North American Free Trade Agreement. Mr. Epstein said had come to believe there was something larger and more important: the way one looks at the world. But, he said, everyone will have a line that cannot be crossed. He said he was once discussing this very subject with the neoconservative writer Irving Kristol. “Yes, that’s true. That’s really an interesting point,” Mr. Kristol replied, “except for Israel-Palestine.”

Mr. Epstein also said not all friendships need to deepen, although there is a natural tendency: “We meet, we like each other, we say, ‘Why don’t we get together with our wives and husbands,’ and soon we say, ‘Why don’t we take all our extended families and go to Antarctica together’ — this doesn’t have to happen.”

gshapiro@nysun.com