We say we that we love our romantic partner, our children, and our friends. But, as anyone who has loved all three knows, these relationships are very different.

Do they all have something in common that unites them, that justifies using the same word, love, to describe how we feel?

Consider, too, how greatly romantic relationships vary across different couples. Some relationships are full of passion and sexual intimacy. Others are built on comforting routine. Some couples live together, while others live half a world away. Many couples are emotionally expressive, but some never say the word �love.�

Yet, people in all of these vastly different relationships would say that they love the other person. The same goes for a wide range of parental and friend relationships.

Is the concept of love so loose that it doesn�t mean any one thing in particular? Or, is there something at the core of every loving relationship�regardless of the type of relationship or who is in it?

As it turns out, there is one ingredient that is more important than everything else.

Trust?

Nope. You can love your teenager without completely trusting them.

Emotional intimacy?

This is fairly critical�but for some friendships it�s more important that you enjoy your friend�s company.

Commitment?

That�s a biggie, but not every relationship requires it.

Give up? According to research[1], the one thing that every loving relationship has in common is care for the well-being of the other person.

That�s right. You can respect someone, be intimate with them physically or emotionally, and understand them better than you understand yourself. But if you don�t truly care for their welfare and happiness, then �love� may not be the right word to describe how you feel toward them.

As you might expect, then, the degree to which you care for your romantic partner�s well-being is a good barometer for your relationship. In fact, one of the biggest predictors of falling out of love and ending a relationship is when one person stops caring for the other�s welfare[2].

A couple caveats: First, this research has primarily been conducted with North American samples, but conceptions of love vary across cultures and history. The ancient Greeks, for example, recognized certain kinds of love that wouldn�t be familiar to most contemporary North Americans�such as agape, a kind of universal, unconditional love.

Second, care for the other person�s well-being, while necessary, isn�t always sufficient. Depending on the type of relationship and the people involved, love may require a few other things.

For example, many people consider the following also to be key ingredients for a successful romantic relationship: making passionate and intimate love, being comfortable with each other, and listening to what the other has to say[3].

Which of these other ingredients are beneficial will depend on the type of relationship[1]. For instance, sexual desire is good for romantic love but generally bad for friend love. Exclusivity, important to many romantic relationships, is harmful if you are a parent about to welcome your second child.

But what is always important�what is, in a real sense, love�is caring for the well-being of the other person.

?References?

1. Hegi, K.E., & Bergner, R.M. (2010). What is love? An empirically-based essentialist account. Journal of Social and Personal Relationships, 27, 620-636.

2. Duda, M.L., & Bergner, R.M. (2016). Sustaining versus losing love: Factors discriminating the two. Marriage & Family Review, 1�19.

3. de Munck, V.C., & Kronenfeld, D.B. (2016). Romantic love in the United States: Applying cultural models, theory, and methods. SAGE Open.