Qualitas and Quantitas: two ways of thinking in science

The paper explores the complex history of quality and quantity from Aristotle's doctrine of categories up to current discussions of the status of qualia in the mind-body problem in modern analytic philosophy. In the first part of the paper we trace the progressive mechanisation, mathematisation and quantification of the natural sciences, processes which spread to the humanities and medicine as early as the seventeenth and eighteenth centuries and later culminated in the logical positivism of the Vienna and Berlin Circle. The second part discusses the renaissance of qualitative research methods in the nineteenth and twentieth centuries in the humanities and the social sciences (hermeneutics, descriptive psychology, phenomenological sociology; the Chicago and Frankfurt School). It describes the origin of the terms "quality of life”, "quality of the environment”, "qualitative growth”, etc., and brings out the quite unexpected fact that qualitative research methods are nowadays also in vogue in mathematics, physics and artificial intelligence. The paper is based on a comprehensive search of the databases of several libraries via the keywords "quality” and "quantity”. It contains a bibliography of some 200 item