A thin smile, a bright smile or beamish grin. From infancy we learn that widening our mouths wins approval from the universe of strangers inhabiting the earth, a ticket toward admission. Sycophants or false friends may also smile, even a Ponzi schemer, but that we soon learn to allow for. Smiles then become almost a tic, yet at heart zoom affection between friends quicker than words do.

Since we have no tails to wag we smile, with an assortment of intentions from solace to advancement, schmooze to sleaze. People sometimes smile while their foreheads frown, but not as hypocrisy. It is simply life’s crosscurrents that add crinkles and character to an aging face.

Grin and bear it, we commonly say when befuddled. The very habit seems to help, as if endorphins are released. A grimace is a smile gone wrong, but laugh and the world laughs with you, weep and you weep alone. We don’t want downers, and if you’ve got a cold don’t sit next to me. A laughing brook, a smiling sea can be an epiphany. We hope the future smiles. A smile is an enabler or placates: that “winning” smile, as we say. Even a tumid wallet isn’t better.

A baby’s smile can be heavenly; also paleolithic. Its power helps perpetuate the species. And a movie star gamely grins for the paparazzi to maintain basic appeal. Happiness is like a candle flame and we want it pointing up. Half-smiles are okay too, like humming a song. It means you know how to. Singin’ in the rain, etc.

Hypocrites and villains smile; it’s their cheapest disguise. A dubious smile conveys qualifications, a sad smile regret or sympathy and possibly even a prayer. This unconscious kind of eloquence may be the forte of our polite custom of smiling. A nod with the pro forma “How ya doin’?” wouldn’t cut it.

Yet the rictus reflex humans adapted into a grin is also worn by roadkill and living mammals in extremis. People grimace when in pain. Smiles don’t signal undying affection but simply recognition for whatever ambivalent purpose. When equivocating we smile. Both invitations and dismissals may accompany a smile. Those who haven’t learned to smile are automatically handicapped in personal and professional life.

Smiles affirm let’s talk. Guileless, sly, sarcastic, altruistic and full-hearted, they come in many colors, though “smiley” is not a flattering description of a person you expect to meet.

God forbid a world without children, family and friends who grin. We depend upon it, just as on a smiling sun. Good fortune, we say. Ignore the hypocrites. No fight-or-flight hormones are triggered by a smile.

Crocodiles smile and the Cheshire Cat, Halloween pumpkins and that “What Me Worry?” Mad Magazine clown. Smiles flicker and flash. Now you see them, now you don’t. Poker-faced, we discipline naughty children or neglectful adults. Smiling requests patience, requests humor and understanding. Grim or grinning, yet lackadaisical may win the day lit by a lightbulb smile. The orifice with which we eat also gives us voice and is our main emotive tool of silent expression.

Woe is a downturned mouth, but kisses prelude torso grinding — creation preceding the act of creation.

A smile is a password, a passkey everybody acquires but may not use. Aginners and squabblers don’t, although it’s such a convenience and miniscule in cost. Hope and gladness are advanced.

“The cat’s meow,” we used to say when there was some small triumph to celebrate. That era when animals figured more in speech, as in “there’s more than one way to skin a cat,” confused people were “buffaloed,” a messy room was “a pig sty,” and an old man was an old goat.

A smile cracks open a door; yes, you can speak to me. It’s the least taxing of introductions, the opposite of huffy or choleric. A smile is an aperture you can bypass or pass through. Our words and tone span infinite variety. Though generally we take a smile to be a sign of decency or even empathy, a louse may smile because he screwed somebody and made a killing, or saw them spill hollandaise all down their best suit.

Smile for the photographer, we suggest, as an indicator of both health and good sense. But those many lines creased into our faces do register how much and in what ways we lived.

Edward Hoagland is the author of over 20 books and hundreds of essays. He lives in Edgartown.