There is very little difference between the method of arranging these intervals for strings and that given for sixths. The type of adaptation will be determined by the style, tempo, and dynamic of the passage in question.
Similar treatment can, of course, be applied to broken intervals in the tenor and/or bass ranges as shown in Examples S-6c and d. The versions given at Examples S-6a and c are called for in fast tempos while those at Examples S-6b and d are playable in most moderate and slow tempos. (See the second movement of Beethoven's Sixth Symphony for string parts in broken thirds.) The upper eighth-note stems (cello) in Example S-6c have an alternative modification which permits a legato effect for broken intervals at fast tempos.
Continuous legato thirds are possible only when arranged as indicated at (1). This contrary-motion principle, if applied to repeated chords (Fig. S-lb), will allow the full chord to sound with legato phrasing.