The normal-state thermoelectric power of the high-{ital T}{sub {ital c}} superconducting cuprates shows a systematic but unusual dependence on temperature and on the concentration of holes in the CuO{sub 2} planes. In this paper it is shown that the observed pattern is predicted within a conventional Fermi-liquid picture and follows from the observation, already inferred from thermal-conductivity data, that the acoustic phonons remain scattered predominantly by electrons up to room temperature.