The String Quartet No. 2 of Leos Janacek has acquired an extramusical life in recent years. Now a favorite subject for social historians and psychologists, it often appears in programs wherein the management has assumed that an entire evening of music will not be enough to hold an audience’s attention.

Thus this passionate ode written by a man of 74 to the 36-year-old object of his desire (whom he met when she was 25) is combined with readings of their epistles, or else becomes fodder for thespian presentations. Apparently, Janacek’s subterfuge in changing the name of the piece from “Love Letters” to “Intimate Letters” was not enough to quench the public’s interest in its subtext.

Kamila Stoesslova was indeed an exotic beauty – Jewish, dark, with a hint of the Gypsy – and the composer of this white-hot music takes only seconds to introduce her in the viola part, which employs a recognizable Romany scale. The exoticism of the work as a whole owes its spicy flavor to the flutterings of the septuagenarian’s heart at a time when he was obsessed with thoughts of aging. As a statement of yearning, it rivals the steamiest efforts of Franck or Wagner.

The piece was the subject of Rob Kapilow’s lecture at the Walter Reade Theater on Monday evening. As in other installments of his What Makes It Great series, Mr. Kapilow discussed this piece of music and offered examples for his arguments at the piano. The group that later performed the entire work, the Alexander Quartet, supplemented the lecture by sharing individual passages. This is a particularly effective and winning formula.

A show of hands indicated that almost all the audience members were unfamiliar with the piece, but none of them can now make this claim. Mr. Kapilow is a born educator. An enthu siastic and diminutive fellow, he is especially adept at physically following the music around the quartet, making it instantly intelligible for the uninitiated. He is also able to discuss music on two simultaneous levels, thus satisfying neophytes and sophisticates alike. In this lecture, he adroitly explored Janacek’s colorful ability to move from the diatonic to the pentatonic, but assured those in the audience who may not be conversant with these terms that all they really needed to do was “get it in their ear.”

I was particularly intrigued with Mr. Kapilow’s distinction between “together” and “at the same time,” an extremely important, though overlooked, musical concept. The ending of the second letter’s Vivace section, enunciated by the quartet, was a per fect example of how players not performing together can be a positive trait.

After intermission, the quartet (Zakarias Grailo and Frederick Lifsitz, violins; Paul Yarbrough, viola; Sandy Wilson, cello) performed the entire piece straight through. This rendition was the polar opposite of the one offered by the Pacifica Quartet at Alice Tully Hall last Wednesday. Not better nor worse, mind you, but thoroughly different.

Where the younger Pacifica players exaggerated the ponticello effects – that is, bowing near the bridge – the Alexander group did a more polished job of integrating them into the work as a whole. Where the Pacifica was exuberant, the Alexander was measured. Considering that this piece is all about age difference, this contrast was especially relevant.

The Alexander has a big sound that would be perfect for Beethoven. But Janacek requires more delicacy, less bombast. Eloquent understatement was missing in both recent performances. Still, this was a solid effort.

The Alexander players expertly gave the erratic dances of the final missive just the right sense of being offkilter. It is this rhythmic awkwardness that leads to the final thoughts of death, of being out of sync with the universe. This is extremely difficult music to pull off, but the Alexander ensemble rallied for a thrilling conclusion. And we all knew it because we had just learned about the piece’s nuances.

I would love to attend a lecture by Rob Kapilow about a piece I do not like. I have the distinct feeling that I would come away with a newfound and delighted appreciation.