This book presents a synchronic and diachronic investigation of two derivational English affixes. The suffixes -age and -ery are analysed on the basis of dictionary and corpus data and an adapted semantic map method is introduced as a new way of accounting for the semantic structure of derivatives. This study shows that the semantic structure of morphological categories can change signi ficantly over time, and that semantic maps can represent this change in a straightforward manner. The semantic maps visualise the relations and interdependencies of the readings expressed by derivatives, which leads to a new understanding of the semantic complexity of these categories.