Rachel Bayefsky develops a diagnosis (D) to evaluate whether anti-skeptical arguments are circular. D is based on Robert Nozick's account of knowledge as subjunctive conditionals. Bayefsky applies D to arguments against skeptical hypotheses like Descartes' proof of clear and distinct perceptions. She argues D explains how circularity undermines an argument's effectiveness by requiring the conclusion be accepted before premises. Bayefsky uses D to analyze arguments that may seem circular but are not obviously so, like arguments responding to suddenly doubting solid ground or a blind person gaining sight. D clarifies when and why the acceptance of a conclusion must precede a premise, making an argument ineffective.