The late J.L.Austin's influence on contemporary philosophy,which ranked with that of Wittgenstein,was substantial during his lifetime and has grown greatly since his death.He was descrbed as'one of the most acute and original minds that England has producde'. His 1955 William James Lectures,delivered at Harvard University,were first published in 1962.For this second edition the editors returned to Austin's lecture notes and their revisions make this a clearer and more faithful record of Austin's works. The lectures set out Austin's conclusions in the field to which he directed his main efforts for at least the last ten years of his life.Starting from an exhaustive examination of his already well-known distinction of performative utterances from statements.Austin here finally abandons that distinction,replacing it by a more general theory of 'illocutionary forces' of utterances,which has important bearings of a wide variety of philosophical problems.