Blame an English poet. The word "soulmate" is younger than you'd think. The first known use comes from Samuel Taylor Coleridge, who in an 1822 letter advised a young woman that "to be happy in Marriage Life… you must have a Soul-mate as well as a House or a Yoke-mate." Romantic, right up until you notice he's ranking it just above a good roommate. And here's the twist: the word he coined then basically sat on a shelf. "Soulmate" didn't become the word we swoon over until the 1980s.

The idea, though, is ancient. It starts, as these things do, at a party.

In Greek philosopher Plato's Symposium, written around 380 BCE, a group of Athenians take turns making speeches about love and its meaning. When it's the comic playwright Aristophanes' turn, he spins a myth: humans, he says, were once round creatures with four arms, four legs and two faces, so strong and so cocky that they tried to storm the heavens. Zeus, unamused, sliced each of them in two... And ever since, every one of us has wandered the earth looking for our missing half. That's it. That's the origin of "you complete me," roughly 2,400 years old.

Here's the part the greeting cards leave out: Plato didn't buy it. Aristophanes' story is meant to be charming and a little absurd, and later in the Symposium Socrates gently overrules it because real love, he argues, isn't about clutching your other half but reaching for something higher. Reaching for beauty, goodness, truth, if there's such a thing. So the most famous soulmate myth in history was pitched, in its original telling, as the immature theory of love.

Other traditions arrived at the feeling by different roads. In Jewish thought there's bashert, Yiddish for "destiny" or the belief in a partner meant for you. The Talmud puts it vividly: forty days before a child is even formed, a heavenly voice announces whom they're destined to marry.

So, is the soulmate real, or a beautiful thing we made up?  

I think it's real. And if you think about it rationally, it actually makes a lot of sense. Your soulmate, your other half, is someone who completes you by way of complementing you. But here's the key difference: it isn't just one person. It can be many. All these people, all these potential partners, have one thing in common. They give you something you don't have, and you give them something they're missing in return, whether that's patience, security, passion, gratefulness. Perhaps that's why we say opposites attract: they're complementary, necessary, they balance each other out. True love is that which exists between the sun and the moon, night and day, cold and warm. It's everywhere we look. So maybe they're everywhere too, our soulmates. Yet we struggle to see it because we're so focused on the high or low, rather than the balance, that which can only be created by two counterpoints.