Pierre Boulez's string quartet (Livre pour quatuor), which has been reworked several times, raises specific problems linked to rhythmical notation, metrical displacements, metronomical marks, irrational values,... The aim of this paper is to compare, in a philological perspective, the different states of the score and to define criteria of adaptation. Such criteria both tend to attenuate the quartet's proverbial complexity and try to restore the musical meaning inscribed in the subtle articulation of the rhythmical figures.