This paper argues that critical mathematics education requires reflective knowledge, which lies outside of mathematical and technological knowledge, and which can be generated through philosophical inquiry in the classroom. Philosophical inquiry can provide "thinking tools" for questioning, challenging and critiquing implicit assumptions and misconceptions and for the reconstruction of concepts. As such, it can offer a space for critical reflection on mathematics, for the development of an epistemological approach that encourages an enriched, overarching view of mathematics and its connections to the other school disciplines, society and self. It also offers space for the deconstruction and reconstruction of beliefs about mathematics as a form of knowledge, about the social value of mathematical practice, and beliefs about oneself as a mathematics learner/thinker.