Beethoven's cello sonatas are not often done as a complete, chronological cycle: They run too long for a single concert, but not long enough to fill two concerts without adding some of the composer's non-sonata cello works, diluting the sense of progression in his musical thought.

When performed in close to optimum, single-concert circumstances by cellist Efe Baltacigil and pianist Benjamin Hochman on Thursday at the American Philosophical Society, the sonatas came off as a motley collection - verbose in the early works, oblique in the later ones, and with a clear-cut masterpiece in the middle, the Cello Sonata No. 3 (Op. 69). This is not to say the concert was a misbegotten idea, but to indicate what the performers and Philadelphia Chamber Music Society audience were up against.

Whether or not Baltacigil is a Beethoven specialist, he suddenly seemed like one during his years as the Philadelphia Orchestra's associate principal cellist. A 2005 snowstorm forced him to step in for the absent orchestra with an impromptu performance of Beethoven's Cello Sonata (Op. 5 No. 1). The public was reportedly stunned by his elegant mastery.

On Thursday, the more cumulative impact of playing all five sonatas left you wondering why he moved on to the principal cello seat of the Seattle Symphony Orchestra. As fine as that group is, Seattle isn't the first place one thinks of as broadening one's international profile.

Among the Beethoven sonatas, the biggest hidden challenge is the final sonata - Op. 102 No. 2, specifically the slow movement. Late Beethoven can be terse, but this section operates according to a harmonic plan that doesn't readily reveal itself to the naked ear. It is outwardly held together by thematic content that feels merely functional, leaving long spans of music that go deep into uncharted territory, like that last mile to the summit of a mountain hike, when the end seems to be in sight but keeps receding into the distance.

Here, Baltacigil and Hochman were at their collaborative best. They maintained a solid train of musical logic that also revealed Baltacigil's hallmark: He sustained vivid expression amid playing soft enough at times to seem like an exhalation.

The Op. 69 performance had particular conceptual strength. Cellist and pianist chose a darker palette to set off the piece's intense, concentrated lyricism. Within that, each musical paragraph had distinctive character, the opening section having curious touches of cello portamento (I'm not sure to what purpose), followed by a second section revealing Baltacigil's peerless legato and how meaningfully he uses it.

Performances also embraced Beethoven's extremes. Though the earlier sonatas seem like youthful acting out, the later ones were colored differently, like some conquering hero with bipolar disorder.

Contact David Patrick Stearns at dstearns@philly.com.