Pianist Sergey Schepkin and violinist Robyn Bollinger brought exceptionally evocative performances of Bach’s Six Sonatas for Violin and Keyboard as part of the Glissando series celebrating the composer’s 333^rd birthday. Exploiting Bach’s innovative move to give both instruments equal melodic weight, Schepkin and Bollinger accomplished a very subtle feat at First Church Boston on Sunday, as they kept the duo sonatas at all times firmly anchored in a distinctive aesthetic of dialogue by allowing the violin and the piano to interact as separate and distinct voices, never losing independence of parts. But they also allowed both voices to deploy a surprising range of inner moods. At times, Bollinger’s violin spoke like a limpid and pure flute. At other times, it mourned as a cello. Schepkin’s piano, in turn, sparkled, brooded, laughed, wept, sang, provoked, coaxed and consoled. The two musicians set aside questions of historical (period) interpretation (we heard no harpsichord or gut viol) in order to focus on interpreting the vertiginous complexity of the score.

Both Schepkin and Bollinger deployed a variety of techniques, exploiting the full range of possibility of modern instruments. Sometimes they nodded to historic practice:  Schepkin at times favored a secco touch at the piano, recalling a harpsichord, and Bollinger restrained vibrato judiciously. At other times, the romance of the music called forth rubato and flourishing vibrato. Bach’s music and the litany of performers who have explored these treasuries of emotion in depth guided their  fidelity throughout—not to one school of playing, but rather to the score.

They opted for a fresh, cutting-edge, perennial Bach experimenting before us with the musical possibilities inherent in the duo form. Poised between the deep interiority of Bach’s solo pieces and the convivial rapture of the Brandenburg Concertos, Bach’s duo sonatas combined intimacy and mutuality in a memorably sui generis way on this occasion.

In their interpretation of the first three examples, in sonata di chiesa form with four alternating movements (slow, fast, slow, fast), Schepkin and Bollinger seemed to emphasize the amazing variety in content that Bach was able to infuse into the standard tempi. In Sonata I in B Minor (BWV 1014), the first slow movement was solemn and majestic, whereas the second slow movement rose tenderly upward, like a veritable love duet full of delicate pastel colors, almost Mozartian. Similarly, the two fast movements made a marvelous study in contrasts. The first fast movement, marked by Bollinger’s flute-like violin, evoked a joyful but competitive dance, with each instrument leading in turn, and ending on a beautiful unified cadence, whereas the second fast movement, summoned edgy, fugal, darkness, with dizzying telluric voices verging on the sorts of nebulae-textures that we hear in the Brandenburg Concertos.

A similar variety in the slow movements came across in Sonata II in A Major (BWV 1015). The deeply serene opening movement pleased with its intense disquiet of spiritual intimations. The second slow movement then disclosed something solemn and dusky in Bollinger’s violin, brightened by deft touches of light from Schepkin’s piano. In Sonata III in E Major (BWV 1016), Bach seems to have explored the nocturnal possibilities of slow tempi. The first adagio opened to a vast and silent and sublime starry night, while the second adagio (a chaconne making use of the Phrygian bass) fully awoke to a personal, plaintive, and imponderable mystery.

Similarly, no two fast movements conveyed the same content, and Schepkin and Bollinger brought to the fore the singularity of each example. In Sonata II, for instance, the contrast between the two fast movements was especially marked. In the first fast movement, Bollinger’s violin shone as bright as brass, while Schepkin’s piano rippled swiftly and open-endedly, as though each instrument were keeping up with the other, superseding the other at times, then falling back and catching up again. The second fast movement, in contrast, was all about categorical affirmation and reaching closure, inevitable as truth.

Schepkin noted that the contrapuntal density increases after the two first Sonatas, culminating in the second movement of Sonata IV in C Minor (BWV 1017) and in Sonata V in F Minor (BWV 1018). Thus the second-half found deeper expressivity in enriched complexity. The opening slow movement of Sonata IV came across as immensely moving, meditative and imploring, pervaded by a sense of exposure to alterity. The intricate second-movement Allegro evoked our human yearning to give beauty and form to the watery element of our fleeting world, creating music and fountains as wellsprings of ethereal stability among us. The ensuing slow movement was largely elegiac, with a cello-like violin. The celebratory and capacious final fast movement reached out to earth, fire and air for a plenitude of life, motion, fertility and renewal. Sonata V took us from a poignant lament to a defensive state of stoical sublimity and then to a more viable stance as Schepkin’s piano tenderly coaxed Bollinger’s aching violin into inhabiting our imperfect destiny.

The concluding Sonata VI in G Major (BWV 1019). Comprising five movements, is basically a modified sonata di chiesa that is preceded by a fast movement. The players rooted us in our earthly condition, praising all things terrestrial. They gave the opening allegro movement a sophisticated folkloric aesthetic à la Watteau. The ensuing slow movement, marked largo, evoked the deep repose of nature when it is heavy with crops and cattle, preparing us for Schepkin’s cembalo solo fast middle movement, evocative of the mysterious “plastic nature” that, according to 18^th-century philosopher, sustained life in all things and music in the human soul. After a soulful adagio celebrating the silent life of plants and trees, the duo gave the concluding allegro movement the feeling of a Lӓndler, embracing the pull of gravity that keeps us together on earth, in dialogue, holding hands to dance and to plant the next harvest, far from the noumenal spaces where we lose touch.

Bollinger displayed a technical mastery of her instrument in all of its shades and nuances; her captivating tone prevailed throughout, from warm and singing to quietly incisive to sonorous profundity. Combining a wisdom of fingerboard articulation and bowing techniques, this violinist made us all take note.

Schepkin had clearly imbibed the manifold insights of his predecessors. His global, ecumenical interpretations maintained satisfying fidelity to the governing musical ideas of phrase and counterpoint, and a keen awareness of multiple voices.

Reveling in the difficulty of the score, Schepkin and Bollinger departed with Bach into realms of emotions and textures, guiding us through one of the master’s richest landscapes.

Anne Davenport is a scholar of early modern theology and philosophy. She has published books on medieval theories of infinity and Descartes. Her most recent book is “Suspicious Moderate” on the life and works of the 17^th-century English Franciscan, Francis à Sancta Clara.