Knowledge representation research is not only formal, it isalso descriptiveand normative. Its aim is to implement aformal system which captures a practically relevant body ofcognitive faculties employed by humans and capitalizes onits technical strength to extend human knowledgerepresentation and reasoning capabilities.In this monograph, the author develops formalisms for hisown notion of a vivid knowledge representation and reasoningsystem, characterized by the presence of two kinds ofnegation (weak and strong) and the requirements ofrestricted reflexivity, constructivity, andnon-explosiveness. The book is based on work carried outwithin an interdisciplinary research project at the FreeUniversity of Berlin.