My brother-in-law likes to listen to something he calls “ugly music.”

This is music with angles, asymmetries and dissonance. I first established my bona fides with him by recognizing a piece of music by its very first note, although it took at least a full second — maybe a second and a half — for the name to gather on my vocal chords and make the passage out past my teeth: “Bartok’s fifth quartet.” I think I shocked him.

Of course, I knew the piece well. For I, too, listen to and enjoy ugly music. And I own and read the score to the Bartok Fifth. Also to many other pieces of music that might be considered by fans of more consonant sounds as “ugly.”

But, I am a firm believer in the observation made by Tom Robbins in his novel, Even Cowgirls Get the Blues, that “The ugly may be beautiful; the pretty, never.”

The “pretty” is conventional; it is bland. It requires no thought or consideration: It just lies there, accepted with lip service paid, but with little active engagement. It is a postcard sunset, a Montovani recording, a symmetrical-faced actress indistinguishable from other symmetrical-faced actresses.

But beauty is an active engagement. You have to actually look or hear. You have to notice. It takes effort on your part. Pretty soothes you into complaisance, beauty wakes you up.

There is a French concept, the jolie-laide, or beautiful ugly. It is most often applied to women whose features are not traditionally good looking, but in concert add up to striking beauty and attractiveness. Think of Cate Blanchett, with that slash of a mouth, squinty eyes and broad nose. Each odd by itself. Blanchett is no cornfed cheerleader. But together the features make up a stunning beauty.

The French have almost a corner on the jolie-laide. Consider Jeanne Moreau. Or Isabelle Huppert. Or Charlotte Gainsbourg. It was her father, Serge Gainsbourg (say “gaze-boor”) who wrote a song about the “Laide jolie laide.” He was no icon of handsomeness himself, although I think many found him irresistibly attractive.

But, I’m not talking simply about feminine pulchritude or masculine formonsutude, but about esthetic beauty, about art.

Consider one of the ugliest paintings ever made, and how unbearably beautiful it is. I’m talking of Matthias Grunewald’s crucifixion from the Isenheim Altarpiece in Colmar, France. The Christ is writhing in pain; his skin is brown and gray, covered in sores; his hands are twisted, his head hung low and grimacing, his ribcage pulled up from his sagging gut, stretching him out, racked; his feet twisted and distorted. Even the cross bows downward from the weight, not just of the body, but of the suffering.

Around him are the mourners, also pulled and distorted, all crying and gnashing their teeth. The landscape behind is dark and barren. There is not a single note of grace in the frame, not a single square centimeter of prettiness. Yet, the painting is unutterably moving. You can hardly bear looking at it, yet, seeing it makes you recognize your own humanity in a profoundly deeper way.

Don’t misunderstand me. I am not saying that only ugliness can be beautiful, but rather, making the case that it can be.

Like that ugly music. Brother-in-law listens to Schoenberg with pleasure. One of the first pieces that turned him on to classical music was Beethoven’s Grosse Fuge — surely one of the hardest pieces to listen to in all the repertoire, but also one of the most sublime.

And it’s not just classical music. He listens to jazz, also, with an ear for the more abstruse and difficult bop. Or free jazz. Let’s face it, Cecil Taylor is not a cocktail lounge pianist. Or Thelonius Monk. That is music proud of its own awkwardness, and uses it for expressive purpose.

One might compare Son House with Montovani. The one is pretty, the other is raw, ugly, powerful. House gets to the gut with the sharpness of a surgeon’s blade. Montovani, no matter how glossy and smooth, is a soporific.

Other ugly music: Tom Waits, grating in voice and peculiar in instrumentation, yet, more satisfying than, say, John Denver. I know, that’s not fair. Sorry. But you know what I mean.

I have a long history with ugly music of all kinds. Appalachia is weighted with ugly music that is beautiful. Consider those mountain Baptist family choirs, singing vibrato-less and consistently just a hair flat, making the most mournful keening. Or the scratchy mountain fiddling of Emmett Lundy. I treasure his few recordings.

Many years ago, I had an LP of field recordings of amateur Spanish brass bands playing for religious festivals, marching down village streets. Sour, scratchy, blaring, they were so intensely beautiful in their ugly way, I came to love them. Alas, the LP is long gone and I’ve never found a digital replacement.

When I was a teacher of photography, one assignment I gave my students was to make a bad photograph. I required that it not be a technical botch, but a bad photograph from conception in the viewfinder. What my students — or at least my good students — discovered, and I already knew, was that if you are paying attention to what you are doing, it is very, very difficult to make a bad photo, because the fact of your attention rules out anything not paid attention to — i.e., the ugly.

It is often said that beauty lies in the eyes (or ears) of the beholder, but I think this saying is basically misunderstood. It is taken to mean something like “To each his own,” or “de gustibus non desputandum est,” but I take it to mean quite differently, and more to the point, that beauty is found in the engagement of mind and senses with the object of perception. In other words, when you pay attention with the focus of someone defusing a bomb, you discover layers of depth and meaning — and therefore beauty — that you might not have suspected. And so, the stains on a concrete sidewalk, layered with fallen leaves and maybe a gum wrapper, will, when observed attentively and with the full engagement of your sensibility, may very well strike you as heartbreakingly beautiful.

This is not just something for pointy-headed esthetes. I have known a farmer who can squeeze a handful of spring soil in his hand and find its loamy odor beautiful enough to bring tears to his eyes. For most of us, it’s just dirt. But to someone who attends to it, it is the essence of existence.

It is the engagement that creates beauty, not the beauty that creates engagement.

And so, when you listen to the Schoenberg Piano Concerto with this sort of eager absorption, you discover a beauty in it that those listening passively, perhaps with the radio on while doing their taxes, can never enjoy, hearing instead only a jumble of disconnected noise. It is not disconnected; it is not noise. It is a carefully created esthetic whole and a thing of beauty and a joy forever.

When I was in high school in New Jersey, I spent as much time as I could in Manhattan, visiting galleries, museums, bookstores and concert halls. And I came to love the Museum of Modern Art. I’d get out of the elevator on the gallery floor and to my right would be Jackson Pollock, Van Gogh’s Starry Night, Pavel Tchelitchew’s Hide and Seek (a painting that primarily appeals to an adolescent, which I was at the time), and beyond those, the the farthest gallery was Picasso’s Guernica, 25-feet wide and 11-feet high.

It is a painting of utter ugliness, not only in subject matter (the Nazi bombing of the Basque city of Guernica in 1937) but also in the angular, distorted and abstracted shapes that make up its design. If one has a shred of humanity, the painting cannot be seen without a welling up in your gorge. It is the prime example in the 20th century of a political painting that is actually an esthetic success. It is Picasso’s shay-doov, and the one piece of art, if we had to choose a single one to represent that century, would be the consensus choice.

It is also profoundly beautiful. While I am pleased that the painting has finally been returned to a democratic Spain, I mourn its absence from New York, from my life. I treasured its palpable presence and its emotional power.

The ugly may be beautiful, the pretty, never.