Every woman knows how hard it is when she puts in serious time with a guy who refuses to commit... until he moves on to his next girlfriend, and then suddenly, he's springing for a rock. Single women assume that a guy will pop the question once he finds someone he's compatible with, i.e., The One. But that's not enough to push him over the edge, according to clinical psychologist Alon Gratch, PhD, author of "If Men Could Talk." What, then, does it take?

"Being ready," says Gratch. "In my 25 years of experience working with men as a relationship therapist, it's 49 percent the right woman, 51 percent his readiness to commit." That means that compatibility is hugely important. But if he's not in a marriage mind-set yet, he's not going to commit to anyone... not even Gisele.

In fact, 81 percent of the married men surveyed by the National Marriage Project said one reason they decided to wed was because it was the right time to settle down.

"Of course, even if a guy is ready to walk down the aisle, he still needs to find the right person," says Gratch. "But he is more likely to meet her once he's in that marrying state of mind." To help us figure it all out, we asked Gratch to explain. Here, he divulges the five factors that make a man want to take the plunge.

The Capacity to Love. No matter how head-over-heels your guy is during the initial honeymoon period of the relationship, it doesn't mean he is ready to commit. A man might fall in love, which requires the capacity to idealize. That means thinking and feeling like his partner and the relationship are uniquely special, enabling him to ignore imperfections, which, in turn, makes him feel valued and special.

Loving, on the other hand, involves connecting with her and wanting to be with her for who she is, not who he'd like her to be.

While it might be difficult to decipher the difference between the two, one clue is the test of time. Falling in love happens early on in a relationship, when a couple barely knows each other. Once they become more intimate and learn more about each other's positive and negative traits and the initial love buzz is gone, a man who is only in love will lose interest. If he truly loves, he'll stay.

Another major telltale sign of real love is selflessness and the ability to care. Does your man make sacrifices for you? Is he able to put your wants and needs before his? Relationships are all about give and take, but love is more about giving.

Being Able to Accept Imperfection. Intellectually, we all know that there are no perfect people and, therefore, no perfect relationships. But it often takes maturity and dating experience to actually believe it.

Take a client of mine, who broke up with a wonderful woman simply because he thought he could do better. A year later, he met someone else, who was also great but far from perfect. After two years of dating, he decided to propose. If he had met her a few years earlier, he would have broken up with her too. But now, he realizes that this is as good as it gets, though it took him several relationships to finally understand that.

Having unrealistic expectations makes it impossible for a man to develop a close bond. If a guy who isn't ready starts getting too close to a woman, he'll look for imperfections, either consciously or subconsciously, to create distance between them and, ultimately, to give him a reason to break up with her.

He Truly Believes in Commitment. Even if a man tells you that he's in it for the long term, you won't really know the level of his staying power until you hit some rough patches. If he's not ready, he won't be able to handle the negative aspects of a relationship, and he'll either shut down -- and shut you out -- or bail. A man who is truly ready to bond will be willing to work with you to try to resolve whatever problems the two of you are having.

He's Sure He Can Be the Man. Even though stereotypical gender roles have loosened up and many men are no longer required to be the breadwinners, a lot of guys still worry, deep down, that they should be... and a lot of women still expect it. So if a guy feels that he can't live up to his -- or his partner's -- expectations, he might put off getting seriously involved to avoid feeling like he's not capable. It's a way for him to protect his ego.

According to the National Marriage Project, 47 percent of men agree that they wouldn't want to get married until they could afford to own a home, and 40 percent would want to be able to afford a nice wedding.

He's Tired of Playing Around. While there's no specific age at which single men are ready to marry (nor do they all mature at the same rate), after a while, going from one superficial relationship to another begins to lose its allure, and they crave a deeper kind of bond with someone.

The Art of the Ultimatum: Three times when it might pay to nudge him a bit

1. He Has a Legit Excuse. If you really think the two of you click but he's stalling because he's temporarily focused on something else, like finishing grad school, give him a firm deadline (e.g., till he reaches his goal).

2. He Needs to Rethink His Priorities. Say he's a jock and you hate sports, but he wishes you had that in common. Is it so important to him that he's willing to risk losing you? (Note: If the answer is yes, you don't want him anyway.)

3. He's Chronically Indecisive. Some guys are reluctant because they can't make a decision. He's not afraid of committing to you; he's just afraid of committing. If that sounds like your man, he might need prodding to get off the proverbial fence. Just tell him that you want him to be in your life, but if he can't make a decision in the next couple of months, you'll have to move on. Warning: If you issue an ultimatum, you better be prepared to stick to it.

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