As an harmonic technique, expanded tonality may act either as a decisive stage in a composer's approach to atonality, or as a means whereby he can preserve the essential hierarchies of tonality itself in a context of pervasive chromaticism. For Schoenberg, the expansion of tonality was a process which did not stop until tonality had been ‘exploded’, chromaticism ousting diatonicism just as new types of chord ousted major and minor triads. For Bartók, as, later, for Britten, tonality could survive even without the triad, without fundamental diatonicism. The use of tonal centres—a tonality of single notes—is the hallmark of Bartók's third string quartet, and the tonal centres control the chromaticism, harmonic progressions functioning non-systematically but logically in terms of the schemes of tonal conflicts and relationships appropriate to the work.