Pianist Jeremy Denk plays his PCMS program like the MacArthur ‘genius’ he is, with a John Lithgow coda

Pianist Jeremy Denk has as much stamina for talking about music as he does for playing it. And that’s a lot.

His Philadelphia Chamber Music Society concert on Thursday was actually a lecture recital — encompassing Schumann and Brahms, but with a surprise contribution from actor John Lithgow — in a program that was not anchored by blockbusters but thrived and bloomed in the ongoing context Denk provided throughout.

A frequent Philadelphia visitor, Denk, age 50, is too brainy to do anything conventional, although his deliberate, thoughtful manner never had him wearing his MacArthur Foundation “genius” grant on his sleeve.

I would have preferred to be among the concert’s small in-person audience. But on a cold, rainy Thursday full of scheduling conflicts, I was happy to follow on live stream Denk’s exploration of classical music’s most famous love triangle.

He started with the mentally ill composer Robert Schumann (represented by his youthful, charming Papillons Op. 2), followed by Schumann’s pianist wife Clara coping with her husband’s attempted suicide, in Three Romances, and concluding with Johannes Brahms (who was infatuated with Clara) looking back in Klavierstucke Op. 119 at a lost emotional life.

Amid the program’s cradle-to-grave arc, the concert’s seeming outlier was Missy Mazzoli’s 2013 Bolts of Loving Thunder. In fact, the piece fit in well, turning Brahms inside out in a speculative exploration of his inner turbulence that appears in more filtered form in his own music.

She gave Brahmsian rhythms a heightened edge. Sonorities were more penetrating. Were she writing the piece today, it would probably be more succinct; she has evolved. As is, it led organically to Brahms' Op. 119 — played by Denk not with the luxurious sonority favored by many pianists, but (in the spirit of Mazzoli) without a sonic smoke screen and with more externalized passion.

Clara Schumann’s music made unusual impact, partly because Denk described the state of the couple’s household, with her Three Romances emerging like a diary in reverse chronology.

The first piece was written after Robert threw himself into the Rhine, portraying a shattered world with Denk’s distinctively searching tempos. The other romances, written before the tragic event, had much exterior charm — reflecting life as it never would be again.

In contrast, the more carefree inner dialogues of Robert’s Papillons was played not in light of what the composer became but who he was at that time.

Denk favored a lightly articulated piano sound, a color palette that felt more decorative than profound, lots of youthfully heaving tempos, and a manner that was open-hearted but not sentimental. Historic recordings of Clara Schumann pupils had many of the same interpretive earmarks (namely Robert’s Scenes from Childhood played in 1929 by Fanny Davies).

Denk probably knows those recordings (he does know everything) but since he plays music as if possessed from within, I’d bet he arrived at his Papillons interpretation on instinct.

The performances registered well amid limited but effective camera angles and a vibrant acoustic, thanks to smart microphone placement in the somewhat dry American Philosophical Society — and my Harman Kardon headphones.

In a post-concert session, Denk fielded questions from the far-reaching American Philosophical Society membership that included Lithgow, who presumably watched from home.

He asked if there was anything in Denk’s life that he regarded as a failure. Denk’s answer was extensive. Those who really want to know can access the on-demand concert, which will be available free through 10 p.m. Sunday at pcmsconcerts.org/concerts/livestreams, with a pay-what-you-wish donation requested,