Movement I - Measures 13 to 16

Measure 13 begins the modulating bridge:

The tenor voice drops below the range of the viola. So, in the transcription below, I have raised the tenor voice an octave. As in the opening of the movement, I ignored the octave doublings on the third beat of measures 13 and 14.

The audio sample backs up to measure 12, so you can hear how measure 13 is approached.

Beethoven, in measures 13 and 14, gives the tenor part to the second violin and has the viola doubling the cello an octave higher. Presumably the open tenth in my transcription was not the sound he wanted, so he used this technique to preserve the thirds. Also, as at the beginning of the movement, he adds a chord to the downbeat, providing a smoother transition from the previous measure. Unlike at the beginning of the movement, he uses the same chord on this beat as in the rest of the measure. That suggests his reason for included the chord was not so much to articulate the downbeat as to provide continuity..

Note that he has the viola play an F on beat three of measure 13 even though the second violin and cello have a rest, thus slipping in the octave doubling of the melody in the piano version. A nice attention to detail.

In measure 15, he abandons the eighth-note chords of the piano version and keeps the eighth-note motion only in the cello, which produces a cleaner sound. He also chooses to double not the melody but the middle voice.

Finally, he adds a rest to the cello part in beat three of measure 16. Perhaps he felt the sforzando provided sufficient articulation to this beat. In the piano, the sforzando is not possible, so he included the F-sharp in the bass for extra emphasis.