It is a common intuition that at least in some cases disagreement has skeptical consequences: the participants are not justified in persisting in their beliefs. I will argue that the currently popular non-dialectical and individualistic accounts of justification, such as evidentialism and reliabilism, cannot explain this intuition and defend the dialectical conception of justification that can explain it. I will also argue that this sort of justification is a necessary condition of knowledge by relying on Craig's genealogy of the concept (...) of knowledge. I will then respond to the accusation that the dialectical conception leads to radical skepticism. My response is partly concessive. It does lead to skepticism in areas where controversy prevails, such as philosophy, politics and religion, but this sort of skepticism is quite intuitive. Finally, I deal with the objection that my defense of skepticism about philosophy is self-refuting. (shrink)