Though the subject of this work, "nominalism and contemporary nom inalism", is philosophical, it cannot be fully treated without relating it to data gathered from a great variety of domains, such as biology and more especially ethology, psychology, linguistics and neurobiology. The source of inspiration has been an academic work I wrote in order to obtain a postdoctoral degree, which is called in Belgium an "Aggregaat voor het Hoger Onderwijs" comparable to a "Habilitation" in Germany. I want to thank the National Fund of Scientific Research, which accorded me several grants and thereby enabled me to write the academic work in the first place and thereafter this book. I also want to thank Prof. SJ. Doorman (Technical University of Delft) and Prof. G. Nuchelmans (University of Leiden), who were members of the jury of the "Aggre gaatsthesis", presented to the Free University of Brussels in 1981 and who by their criticisms and suggestions encouraged me to write the present book, the core of which is constituted by the general ideas then formulated. I am further obliged to Mr. X, the referee who was asked by Jaakko Hintikka to read my work and who made a series of constructive remarks and recom mendations. My colleague Marc De Mey (University of Ghent) helped me greatly with the more formal aspects of my work and spent too much of his valuable time and energy to enable me to deliver a presentable copy. All remaining shortcomings are entirely my responsibility. I asked Prof.