They’re all around us, throughout our neighborhoods and elsewhere. Some we may see every day, heading home from work or getting on a bus or walking a dog. They show up at all hours wherever we go.

They’re the strangers we know, all the people we recognize, day after day and year after year, without ever exchanging a hello, much less a smile or a wave. As we go about our business, these passersby become elements of our everyday environment, the scenery that surrounds us.

I see this one guy in our apartment complex who goes out almost every day to run errands. Because he is ubiquitous, my wife and I dubbed him Hugh Biquitous.

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Hugh and I have passed each other on the sidewalks and streets umpteen times over the decades. He looks at me, I look at him. Yet neither of us says a word, let alone stops to chat.

So it is with others I regularly see. The woman who flits around early in the morning sprinkling water on our shrubs. The old man who toddles to the office every weekday carrying his briefcase, even though his entire torso leans to the left. The window-washer with the extra-long squeegee who swabs away at storefronts along our commercial stretch.

We all “know” such people, those the social psychologist Stanley Milgram in 1972 called “familiar strangers.” That’s life in the big city, populated with these human landmarks. It compromises a kind of community, a hidden network.

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Most of us adopt certain attitudes and behaviors among strangers, if only to preserve our sense of privacy and anonymity. Strangers typically engage in the ritual of looking at each other, then sharply turning away. Sociologist Erving Goffman called this “civil inattention,” the act of acknowledging the presence of others without wishing further contact.

This phenomenon of mutual disregard is hardly tragic. No one can know everyone, nor does any of us even remotely want to. We likely have all the acquaintances we can handle for now.

Then again, our choice to remain strangers to the strangers we know may do us a disservice. At worst, we may turn suspicious and paranoid about them. We may wonder whether our next-door neighbor is an enemy.

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Go inside New York politics.

Years ago, my wife and I often saw a man and woman, evidently a couple, strolling around our neighborhood in Queens on weekends, just as we were doing. They saw us, too. But for months all we ever exchanged were glances. Then one day we said, “Hello,” and they said, “Hello” back, and the next time we encountered each other we started a conversation. From then on, they invited us over for dinner every New Year’s Day for more than 10 years.

Every friend starts as a stranger.

Come 2016, maybe I’ll start a habit regarding the strangers I know. Maybe I’ll greet Hugh Biquitous with a cheery hello. He’ll hear my voice for the first time, and perhaps I his. My big social experiment for the year.

Now this gesture of congeniality may well accomplish precisely nothing. Hugh might consider me presumptuous or delusional. He might wonder whether I’m running for president and scrounging for votes.

Hey, at least I will have tried.

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Make of all this what you will. But let’s ask ourselves. What if, contrary to current practices, we all promised ourselves to do the same? What would happen?

I’ll tell you what. We’d come together just a little. The strangers we know would be strangers no more.

Bob Brody, an executive and essayist, is the author of the upcoming memoir, “Playing Catch With Strangers: A Family Guy (Reluctantly) Comes Of Age.”