Constructivism provides insights into the possibilities and limitations of recognizing reality. In light of recent findings in brain research, constructivists advocate for a relativism of truth. They ultimately exclude the objective recognizability of reality. Additionally, they express doubts about the existence of an external world in itself. It can be perceived as troubling that constructivists, in this context, distance themselves from critical rationalism in a factually incorrect manner and misrepresent it in part. In contrast to constructivists, critical rationalists maintain the assumption of the existence of a reality and the possibility of its objective recognizability. The inappropriate simplifications and assumptions made by constructivist authors provide a reason to engage more deeply and clarify the controversy between these two epistemological positions from a critical-rational perspective. Reading this book is helpful for readers who do not wish to explore all facets of the controversy in the literature themselves and want to be informed in a manageable form and with reasonable effort.