What if there were no objective facts, no objective truth, no objectivity at all, only our belief in them? What if our consciousness itself is an unconscious invention, constructed out of logic and language? In this thought-provoking volume, Lynn Segal describes how the ideas of Heinz von Foerster compel us to explore the question, "Do we discover the world or do we invent it?" and suggests that we must first know how we think before we can claim knowledge of the world. The resulting philosophy, Constructivism, examines the limits of what we can know and argues that understanding these limits can lead us to be more responsible for our personal and collective behavior.<BR>After tracing the historical transition from religious belief to a belief in science, Segal examines objectivity from semantic, philosophical, and neurological perspectives. Segal shows that we can never achieve objectivity and that the scientific method ensures only a consensus among observers. Next, he details how language and logic unwittingly predeterime the very conclusions we derive when we try to know the world. Finally, he describes a computational model of cognition that does not depend on first positing the world to account for cognition and consciousness.<BR>While Constructivism may seem relevant only to those in the cognitive sciences, it is, in fact, highly relevant to everyone. Paradoxically, grasping the limits of our own understanding can free us to live more creative and meaningful personal and professional lives.