With an intelligent couple, it ought to be possible for the husband or wife to look for satisfaction outside the relationship - while always taking the partner into consideration, meaning acting openly but still discreetly.

Perhaps the couple got married at 25 and now they're 45 and this is an option. And if a couple is still together, or perhaps finds its way back together, I like to say that it's forever. They belong together, it's a good fit, it's the right pairing. It almost gives me goose bumps.

There are many options in a marriage. If the couple has been together for a certain amount of time and has a certain amount of liberalism or life experience, it could be the kind of relationship in which one partner ventures into the occasional affair, which is then forgiven. This only happens every 13 years on average, but it obviously does occur.

Just go to an auto show, and you'll see all the signs of sexual arousal in the men: shiny eyes, tremors, sex flush. An acute example of the need for professional sex research.

Aura of the mysterious is a minor perversion that a couple shares. A fetish that one of the two partners finds arousing, or a particular sexual scenario. Fantasies have to remain dirty. Cleanliness, scrupulousness and rationality are poison for eroticism.

The social problem is that we haven't come up with any alternative models. Our culture hasn't developed an ars erotica. Think, for example, of conditions in India or in Japanese culture and of how the erotic has been cultivated there. They're not as clinical and rabbit-like as we are.

Some 95 percent of all sexual contact still occurs in permanent relationships. That's an impressive number.