Ihis book offers a new approach to the theory of change in argument structure and voice morphology. It investigates the diachrony of transitivity, and especially the changes in causative verbs and transitivity alternations, based on data mainly from the Greek and English diachrony (all historical data are transcribed and accompanied by glosses and translations into Modern English). Data from earlier periods provide new information on burning questions in both Historical and Theoretical Linguistics. The study shows that (a) causativisations are the result of reanalysis of intransitive verbs as transitive on the basis of the linguistic cue of Case; (b) the changes in voice morphology do not depend on the derivation and direction of new transitivity alternations. Finally, the study demonstrates that the generalisation that guides the changes in voice demands morphological differentiation of the anticausative from the passive types.