As a couple's therapist with clients from around the world, I have long probed the intricacies of desire in modern love. While much has changed in my 30 years of practice, one line has endured, "We love each other very much, but we have no sex."

The story of sex in committed modern couples often tells of dwindling desire with a long list of sexual alibis. "We're too busy, too tired, too stressed." Does this really explain the death of Eros?

Allow me to ask you a different set of questions I attempt to address in my TEDTalk, to help tease out the nature of erotic desire and its accompanying conundrums:

- Why does good sex so often fade, even in couples who continue to love each other as much as ever?

- Why does good intimacy not guarantee good sex?

- Can we want what we already have?

- Why does the transition to parenthood so often deliver a fatal erotic blow to the couple?

- And why is the forbidden so erotic?

- When you love, how do you feel, and when you desire, how is it different?

Love and desire, they relate but they also conflict. And herein lies the mystery of eroticism. How we straddle our drive for connection and closeness with our quest for separateness and freedom is at the core of reconciling intimacy and sexuality, otherwise called the domestic and the erotic. This was the central theme of my book Mating In Captivity.

Let's play a little word game. If you had to give a verb that accompanies love, what would it be? And what would your verb be for desire? I'll drop a hint: what nurtures love is sometimes the very thing that stifles desire.

nother lead question: When do you find yourself most drawn to your partner, and not just sexually, but in the broader sense? You will notice that one elemental aspect of love is consistently absent in the realm of desire.

We are born sensuous. And we become erotic. It is an intelligence that we cultivate and that stretches far beyond sex education. Erotic intelligence celebrates ritual and play, the power of imagination, and our infinite fascination with what is hidden, illicit and suggestive. In my article "In Search of Erotic Intelligence," I suggest that to play a bit more with the ambiguity that's inherent to communication. Eroticism can draw its powerful pleasure from fascination with the hidden, the mysterious, and the suggestive. In my talk you will see why this matters and how I draw the contrast between sexuality and eroticism.

Yet, a passionate marriage? Now there's a contradiction in terms. Passion has always existed, but mostly outside the conjugal bed. This is the first time in history that sexuality in long-term relationships is rooted in desire, i.e., just because we want it, and no longer a female marital duty and a device for yielding up multiple farm hands. (Here I'm talking about the West.)

Today we want our partner to give us both stability and passion, a sense of belonging and a respect for our individuality. We're asking one person to give us what once an entire community provided. It's a tall order for a party of two. It's not that we're more insecure today, but we bring all of our security needs to one partner. Suffice it to say that couples crumble under the weight of expectations. Fire needs air, and many modern couples struggle with mating in captivity. So what are they to do to sustain the libidinal charge?

In the age of transparency, I find that one of the toughest nuts for couples to crack is how to introduce novelty in the enduring and mystery into the familiar. Lots more to read on my websiteEstherPerel.com and my blog.

At the heart of sustaining desire lies a challenge. It demands that we learn to reconcile our fundamental need for safety and security with our equally strong need for adventure and novelty. We want our relationships to be both, the anchor and the waves. Think of this as a paradox to manage, not a problem to solve.

The poetics of sex draw upon imagination, playfulness, curiosity, focus, and presence to name just a few of the key ingredients.

How is your erotic IQ? What needs attention, renewal, unlocking, healing? Mark your first thought, and your next action.