When you’ve heard a piece of late 18th century music on the radio and you don’t know who wrote it, how do you tell whether it was by Haydn or by Mozart?

A former teacher of mine had a simple answer: “If you can remember the tunes when it’s over, it’s by Mozart.”

They were both great composers, but Mozart — in his best music — had a quality that Haydn lacked: He could write “sticky” tunes.

I’ve lately been thinking about this quality, because while we instantly recognize “stickiness” (that recognition itself is practically the definition of “sticky”), it’s difficult to know why one tune is sticky and another isn’t.

And it is important to recognize that stickiness is only one quality of good music. Some composers, like Haydn, still wrote great music without it. Heck, the composer most people name as the greatest ever — Beethoven — hardly ever wrote a memorable tune. I mean memorable in the way that even a Rodgers and Hammerstein tune can be memorable. Let’s face it, “Da-Da-Da-Dum” is not really even a tune: It’s a pattern repeated so many times in that damn symphony it is pile-driven into our memories. Anything we rehearse over and over can be memorized. Like multiplication tables.

In contrast, the first thing you hear in, say, the Mendelssohn violin concerto is so sticky, if heard once, it is instantly becomes part of your life.

It should be acknowledged that stickiness is not the be-all and end-all of music. Marvin Hamlisch had it and Stephen Sondheim lacks it, but who is generally held to be the better composer? Sometimes, a catchy tune just means a shallow tune. 

There are those composers we instantly recognize for the warmth and catchiness of their melody writing: Mozart, Rossini, Schubert, Dvorak, Tchaikovsky, Verdi, Mendelssohn, Schumann. And there are those whose music finds its strength in other qualities, such as Beethoven, Brahms, Stravinsky.

That stickiness is a distinct quality of music can be seen in the descending careers of both Mendelssohn and Schumann. After Schumann’s breakdown, his music lost its stickiness. It maintained all its craft, but none of its memorability. Mendelssohn wrote the Octet and the Overture to Midsummer Night’s Dream when he was a teenager, but by the time he became the pious paragon of English Victorian culture, he was pumping out some very dull music, indeed. The two composers simply lost their adhesiveness. 

In contrast, two later composers took the other route: Early music by Cesar Franck and by Leos Janacek chuff-chuffs by on sheer force of will, while when their hair turned gray, they were both touched by the sticky muse and gave us music we can’t get out of our heads.

One thing that seems to be true about sticky melodies is that they feel somehow complete in themselves. The secret of most great symphonic music is that it is built on patterns of notes that can be altered and developed, the tune can be taken apart and rearranged, turned upside down, slowed down or sped up, without losing its identity — like Beethoven’s “Da-Da-Da-Dum.” But a sticky tune, like the Mendelssohn concerto, is so complete in itself that it doesn’t easily bear symphonic development: Change a note or rhythm and it loses its identity. This is the downfall of so much music from the Romantic era, where a tune is so good to start with, the composer has nowhere to go with it, so he just repeats it with different instruments or at a different register. It can make for monotony in a 40-minute symphony, a monotony that Haydn never courts, because he is always doing something fresh and new with his themes.

But stickiness isn’t just for music. Some paintings are sticky, even after they’ve dried. Some poetry is sticky, some architecture is sticky.

Just compare, say, Alexander Pope with John Dryden. Pope, sticky, Dryden, dry. All the craft is there in Dryden, and some very lovely turns of phrase, but nothing as memorable as “The proper study of mankind is man.” Pope ranks third as most quoted poet in Bartlett’s.

Keats: sticky. Shelley: not so much.

Wordsworth, like Schumann, lost his youthful stickiness.

Again, stickiness is not the sole measure of worth. Joyce Kilmer’s “Trees” is as sticky as a caramel apple, but not exactly on a level with John Milton.

Claude Lorrain, sticky; Nicolas Poussin, not so sticky. Henri Toulouse-Lautrec is one of the stickiest artists ever. You can come up with your own list of sticky paintings, sculpture and photographs. The subject of stickiness is wide and deserves deeper critical attention.

Stickiness is what every “hook” is in a pop tune, it is the sine-qua-non of a magazine ad or a TV commercial. It may have something to do with simplicity and clarity, but even a complex tune can be sticky.

I would welcome some scientific study of stickiness.