When you think about the qualities found in a true "soul mate" relationship, what one word comes up most often on the top of your list?

Is it CHEMISTRY? Probably.

Just the mention of this term conjures up powerful feelings and images for anyone who has ever been in or seeking a love relationship. It is often described as a feeling that leaves you breathless, excited and weak in the knees. Palms sweat, the heart races and the body tingles with nervous anticipation.

It is believed by virtually everyone that true love cannot exist without chemistry. Therefore, the conclusion most would-be lovers come to is that if they experience these intense feelings towards someone, they have the basis for an ideal and lasting relationship.

Right? Maybe not. For this definition of chemistry is limited to one's physical response to another person. It lacks an entire dimension that resides in our values, beliefs, personalities and worldview.

In order to know you have the right connection with a potential (or existing) partner, it's important to have a basic knowledge of what real chemistry consists of, instead of embracing only the myths that surround it. This can be difficult to do. This intense, physical passion is the stuff that Oscar winning movies and best-selling books are made of. So, take a step back for a minute and see if you recognize yourself in the following.

Sarah is a thirty something, very attractive and successful, professional female. She has been in a relationship for over a year with a man who is unfaithful, disrespectful and incapable (unwilling) to make any commitment to her. Yet, when he makes late night "booty calls", forgets her birthday, or stands her up repeatedly - she remains available and willing, in spite of her general unhappiness and upset over their "relationship". Why? "I think I have mistaken great sex for love. I feel this intense chemistry and physical intimacy when we are having sex, even though he offers me nothing else. Over time, it has left me unhappy and feeling badly about myself."

John is an attractive, intelligent, 30 something male who owns his own successful business. He's dating a woman that he thinks he is in love with. He has knowledge that she has been out with other men. She cancels dates and is often critical and emotionally distant. She refuses to discuss commitment or taking the relationship to the next level. Yet, she turns to John for emotional, physical and financial help whenever she feels she needs it. Why does John continue to see her? "She's beautiful and the sex is great". We have such strong physical chemistry. It's almost like an addiction for me. My friends can't stand her and even I know she's not really a "keeper", but it's hard to walk away.

These vignettes are great examples of how physical chemistry can be mistaken for the real thing. The attraction on one level is strong, yet these are not relationships that have the right elements to grow into happy and satisfying partnerships.

So, what is missing?

Kahlil Gibran defines it as "spiritual affinity". It's the hidden element of chemistry. It's when two beings meet and connect on a deeper level. It can only be felt in the heart and soul. It's about friendship, respect, humor and the feelings of warmth and contentment that come when you are in his/her presence.

People often report finding one without the other. This is understandably a cause of great frustration and confusion about whom should we choose and why. In order to understand this better, it is helpful to know how and when each facet of chemistry occurs.

Physical attraction (or lust) generally begins during our first contact with someone. It can DEVELOP into something more over time, yet some pull is there from the beginning. The chemical that results from this attraction (and intensifies it) is phenyl ethylamine - or PEA. It is a naturally occurring substance in the brain. Essentially, it is a natural amphetamine. It stimulates us and increases both physical and emotional energy. The attraction causes us to produce more PEA, which results in those dizzying feelings associated with romantic love. Another substance that is released by PEA is dopamine. This chemical increases a desire to be physically close and intimately connected.

When these chemicals are being secreted in larger doses, they send signals from the brain to the other organs of the body. If you wonder why you or someone is attracted to the "wrong" person, it may be because you are high on the physical response to these substances, which overwhelm your ability to use your head and exercise "good judgment and common sense".

"Spiritual affinity" develops over time and repeated contact. When these feelings begin to emerge, the brain produces endorphins. These are more like morphine and result in an increased sense of calm that reduces anxiety and helps to build attachment. As relationships move into this phase they are characterized by more comfort, commitment and friendship.

Generally speaking, all "soul mate relationships" require at least some measure of each of these. The important thing to remember is that they come in stages, which is not to say that the physical attraction passes as one moves into a deeper connection. However, it changes. We cannot sustain those intense emotions as we travel down the road to commitment and a shared life. However, in healthy relationships those moments of intensity can and do occur for brief intervals at intermittent times.

Remember not to confuse great sex or deep friendship with romantic love. Instead, look for a measure of both of these in your feelings for another. For then you have the ingredients that lasting love is made from.