This book from the series Notebooks in Metaphysics is addressed to all who investigate various aspects of the reality that surrounds us and want to make realistic philosophy the foundation of their knowledge about the world and man. The author provides an introduction to an understanding of the specific character of metaphysical (philosophical) knowledge and shows the first philosophical interpretations of the reality of the world and man, namely the monistic interpretation, and the dualistic interpretation, and shows the sources, consequences, and contemporary varieties of those interpretations. The book also contains classical texts, which are excerpts from the the pre-Socratics and from Plato.