Excerpt: In this article, we address the key points of contention raised by Chadwick (2004) in an effort to clarify the utility of a specific form of constructivismradical constructivism – as a viable theory of knowing. We believe that radical constructivism is a cohesive and convincing explanation of individual knowing, and we use this theory as the primary framework to counter Chadwick’s accusations about constructivism’s lack of utility and value. First, we identify the various definitions and philosophies of constructivism. Second, we discuss the role of ontology in constructivist philosophy, with special attention to its role in radical constructivism (Glasersfeld, 1995), especially because of its potential for being radically misinterpreted. Third, we discuss the influence of radical constructivist theory on teaching, learning, and curriculum. We conclude by identifying some of the issues that remain unaddressed in constructivism and summarizing the main contributions of radical constructivism to a viable theory of individual knowing.