Challenging existing lexical-semantic accounts, this book presents a compositional approach to factivity and its acquisition. Factive sentences such as >John forgot that he bought wine< presuppose the truth of the embedded complement. The author argues that factivity results from the interaction of lexical-semantic, syntactic, and discourse-semantic factors. Rigorously designed experiments and a detailed analysis of longitudinal corpora provide evidence that the multidimensionality is mirrored in the acquisition process by a stepwise mastery of its different components. This book should be of interest to advanced students and researchers in both theoretical linguistics and language acquisition.