How Millennials Signal Personal Identity Through Brand Preference Burgers or tofu? Fair trade clothing or fast fashion? Millennials are making conscious statements with their purchases.

For most of Western history, people's identities depended on accidents of birth. You could be born a patrician or a plebe, a Protestant or a Catholic, a small-town kid or a city slicker. Whether you were in ancient Rome or 1950s Minnesota, chances were you'd settle down in the town your parents lived in, go to the church or temple your parents went to, vote for the political party your parents voted for. You didn't have to assemble an identity for yourself, because so much of it was already set in stone the moment you were conceived.

Not only were the identities pre-fabricated, they were also very binding. Penalties for leaving your group, your guild, your caste were very high, and if you did manage to leave, good luck getting someone else to take you in. Groups developed not only cohesive identities, but also sets of values that went along with them.

When D'Artagnan's father sends him off to the capital in the Alexandre Dumas classic The Three Musketeers, the old man doesn't tell him to go find himself. Instead he tells his son that he has no choice but to be brave "for two reasons: the first is that you are a Gascon, and the second is that you are my son." He goes on to enumerate all the values he associates with being a Gascon:

Never fear quarrels, but seek adventures. I have taught you how to handle a sword; you have thews of iron, a wrist of steel. Fight on all occasions. Fight the more for duels being forbidden, since consequently there is twice as much courage in fighting. I have nothing to give you, my son, but fifteen crowns, my horse, and the counsels you have just heard.

Related: Tim Ferriss: If You're Not Happy With What You Have, You Might Never Be Happy

With great freedom comes great responsibility.

Today, though, it's unusual -- even insulting -- to imply that someone's identity is defined at birth. People change their careers and their lifestyles at the drop of a hat, and are celebrated for it. The former White House staffer who now hosts a nationally syndicated cooking show? The philosophy student born in a log cabin who now runs a $3 billion tech startup? Both of these career trajectories are not only possible, but highly prestigious and desirable, in a way that they wouldn't have been 100 years ago.

This freedom can be invigorating, but also exhausting. Building an identity from scratch is hard work. And no generation has more building to do than the millennials, the generation with the cleanest slate of identity in history.

Yet when you look at the data, it's hard to see how that building is happening. Millennials tend to avoid traditional affiliations: 50 percent of them don't identify with a political party and about one-third of them don't belong to an organized religion. Contrary to the stereotype of the 30-something who refuses to leave the nest, they aren't tied down geographically. A Mayflower survey found that 59 percent of millennials live elsewhere than their hometown. The rise of the gig economy and pervasive job-hopping means that jobs aren't a consistent source of identity for most millennials either.

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The building blocks of identity.

So how are Mmllennials building their identities? Let's check in with Gigi Hadid and Ashton Eaton, two millennials who just happen to be a supermodel and an Olympic athlete, making small talk during a cover shoot for Vogue.

"Have you had Backyard Bowls?" He turns to me. "It's an açai-bowl shop," he says. "The cool thing is it was started by two guys who met at Santa Barbara City College."

"Of course!" Hadid says, a little aghast, though now she has completely relaxed, which is not easy to do in those stiletto Pumas that Rihanna designed. "I love Backyard Bowls!"

Next, the two new friends engage in an ultrahealthy bowl-flavor duel. Hadid calmly takes a shot. "Berry bowl with peanut butter."

"Spartan muesli!" says Eaton. "I mean, yeah—berry bowl is good. But peanut butter?"

Now it seems that Eaton has passed a sort of Santa Barbara test, and Hadid is joking that she can give him the native Santa Barbara tour.

Backyard Bowls here becomes a proxy for a whole constellation of shared values. Santa Barbara City College: local, down-to-earth, authentic. The açai bowls themselves: trendy, health-conscious. Using the brand as a kind of shorthand, Eaton and Hadid are establishing that they have much more in common than food preferences (though it seems like her Spartan muesli minimalism might conflict a bit with his more decadent love of peanut butter). Eating at Backyard Bowls is as important to their identities as going to church every Sunday might be for someone else's.

It's not just Eaton and Hadid, either. Studies show that millennials are more brand-loyal than any other generation; just over one-half of them say that they are extremely loyal or quite loyal to their favorite brands.

Related: 5 Ways Brands Can Build Loyalty With Young Consumers

But why brands?

The link between branding and identity is deep and long-established. In the 1970s psychologists were already theorizing that buying certain brands helped people "reduce discrepancies between their actual and ideal self," thereby increasing their self-esteem; decades later they are finding in studies that this "self-congruity" was a major factor in brand loyalty. A consumer buys a Ford Mustang because they believe themselves to be -- or want to be -- the type of person who owns one.

But the internet has kicked that feedback loop between branding and identity into overdrive. Millennial consumers don't just seek self-congruity through products that they actually buy: they also seek it through the product photos they pin on Pinterest; the brands they follow on Facebook, Snapchat, or Instagram; the unboxing videos they watch on YouTube. Some commentators have hypothesized that this abundance of social proof is one reason why millennials are so loyal to brands -- it's easier to trust your friends (or social-media influencers) than it is to trust traditional advertising. This, plus the decay of more traditional sources of identity, is the reason brands have become so important in millennials' conversations.

Related: Online Reviews Are the New Social Proof

To reach Millennials, values are key.

What does all of this mean for brands? It means that to remain competitive in today's marketplace, they need to clearly embody the building blocks of identity: values. You see the power of this approach in the current popularity of athleisure: workout clothes that look so good you can wear them outside the gym. Those high-performance fabrics cost a pretty penny, but millennials (and others) are willing to spend. Because they're not just buying the clothes to be fashionable; they're buying them to broadcast the fact that they value a healthy lifestyle full of regular gym trips.

A 2015 Nielsen survey also found that three out of four millennials -- more than any other generation -- are willing to pay extra for sustainable product offerings. Values are the reason millennials wear TOMS shoes and vegan leather, drink fair-trade coffee and locally brewed craft beer. It's also the reason a Boston Consulting Group study found that millennials spent 13 percent more on plane tickets than other generations, shelling out for posh rides on airlines like Singapore Air, Japan Air and Emirates. Millennials tend to value experiences over material possessions, so it makes sense that they'd save up money for a travel-related splurge.

Related: Increase Your Perceived Value With Social Proof -- and Charge More

The easy conclusion here is that branding is important and companies should do more of it. But I would go much further than that. Brands are no longer an ancillary accessory of identity -- they are the core of it. That means that in some cases, your brand won't just be central to your product; it will actually be more important than the product itself. This is both an opportunity and a tremendous responsibility. And, for companies looking to reach millennials, it's also the wave of the future.