Gewirth is best known for his ethical rationalism, according to which a suprememoral principle, the "Principle of Generic Consistency", is derivable as a requirement of "agential self-understanding". The principle states that every agent must act in accordance with his or her own and all other agents' generic rights. According to Gewirth's theory, the PGC, is derivable from the fact of human agency, but it is derivable only via a "dialectically necessary" mode of argumentation. The mode is "dialectical" in the sense that it presents the steps of the argument to the PGC as inferences made by an agent, rather than as statements true of the world itself. Each step is thus a description of what the agent thinks, not what things are like independently of the viewpoint of the agent. This mode of argumentation is also "necessary" both in the sense that its initial premise is inescapable from any agent's standpoint and that the subsequent steps of the proof are logically deduced from this premise. Gewirth thus holds that any agent must accept the PGC as the principle of human rights on pain of self-contradiction because the principle is contained as the inescapable conclusion of any agent's dialectically necessary characterization of his or her own activity. The initial premise, which we all must accept insofar as we perform any actions, is simply "I do X for purpose E." All agents implicitly accept this assertion insofar as they perform any voluntary actions; they therefore must accept it on pain of contradicting that they are agents. From there, Gewirth holds that an agent must attach a positive value to E, through some criteria, that motivates them to achieve E, or else there would be no motivation to act in the first place. Because an agent values E, it follows that they must value the conditions necessary to achieve E. Gewirth claims these conditions are that of freedom, the ability to choose purposes, and well-being, the ability to realize purposes. Since an agent must value their freedom and well-being, it follows that agents have a claim right to their freedom and well-being, for it is mutually exclusive to hold both that they must have freedom and well-being and that they may not have freedom and well-being. Given that each agent has a claim right to freedom and well-being, and that agents accept parallel reasoning, agents must accept that other agents also have those rights. Therefore, agents must respect the freedom and well-being of their recipients as well as themselves, as both groups have the generic rights. While Gewirth admits that his argument establishes the PGC only dialectically, he nevertheless claims that the principle is established as necessary, since any and all agents must accept it on pain of contradiction, and further argues that it is not necessary to establish a moral principle assertorically. In 1991, the philosopherDeryck Beyleveld published The Dialectical Necessity of Morality, an authoritative reformulation of Gewirth's argument including a summary of previously published objections and Beyleveld's own rigorous responses to them on Gewirth's behalf. There is no clear consensus among philosophers regarding the soundness of Gewirth's theory. For at least the past 30 years, philosophers have offered numerous objections to the theory but have nearly all been substantively countered by Gewirth and his adherents. The debate concerning the ideas Gewirth has set forth thus continues. In 2016 Routledge published a volume on Gewirth's ethical theory, edited by Swedish philosopher Per Bauhn and containing contributions by fifteen international scholars. Gewirth's argument bears a resemblance to the discourse ethics type theories of Jürgen Habermas, Karl-Otto Apel, and others. His student Roger Pilon has developed a libertarian version of Gewirth's theory.
