CHICAGO — On Aug. 4, one day after he turns 91, Tony Bennett will take the stage of the Ravinia Festival, in Highland Park, Ill.

If past performances — such as last year’s — are any indication, he’ll perform about two dozen songs from memory. Some will be up-tempo, and Bennett may soft-shoe alongside the piano in swing time, drawing instant ovations for his energy and grace. Many tunes will be ballads, and if he follows precedent, he’ll stretch vocal lines and sustain long notes longer than most people his age, or any other, can.

In the end, he’ll remind listeners of the depth and breadth of his repertoire and his lifelong commitment to what some call the Great American Songbook and he terms simply “the silver lining songs.” Meaning that even at their darkest, these masterworks by George Gershwin, Cole Porter, Duke Ellington, Billy Strayhorn, Jerome Kern, Irving Berlin and others inspire optimism and hope through the sheer poetry of their melody lines, poignancy of their harmonies and eloquence of their lyrics.

Yet the overriding question remains: Why does he still do it?

Why, after more than half a century before the public, does Bennett still feel compelled to jet around the globe, invite comparisons to his more youthful work and, just before showtime, experience “butterflies, right in the little tummy,” as he put it to me in 2013 (when he was a mere 87)? At such moments, Bennett continued, “I just say, ‘I hope everything works.’”

So far, it always has, but why put yourself through this when you really have nothing left to prove?

“I like to make people feel good,” says Bennett today. “I’ve always liked that. I still enjoy doing that. I feel that it’s a gift to be alive, and I just try to communicate that to the audience, that they should all feel very good about their lives.”

Bennett, of course, has been widely lauded for his enormous contribution, the Library of Congress recently announcing that he will be the next recipient of its Gershwin Prize for Popular Song (an honor previously bestowed upon Stevie Wonder, Paul McCartney, Carole King and the songwriting team of Burt Bacharach and Hal David, among others).