His chief work is the Traité de l'argumentation – la nouvelle rhétorique (1958), with Lucie Olbrechts-Tyteca, translated into English as The New Rhetoric: A Treatise on Argumentation, by John Wilkinson and Purcell Weaver (1969).

As a result of his empiricist study of justice, Perelman rejected positivism in favour of philosophies that provided a rationale for value judgments.

In 1948, he met Lucie Olbrechts-Tyteca, who had also attended the Université Libre de Bruxelles, and began collaborating on a project that would eventually establish ancient rhetoric as the foundation for a logic of value judgments.

Undertaken in the spirit of Fregean observation and synthesis, the work analyzed a wide range of actual arguments from the realms of philosophy, law, politics, ethics, and journalism.

In 1962, Perelman was invited by Henry W. Johnstone and Robert Oliver to take a position at Pennsylvania State University as a distinguished visiting professor.

Johnstone created the influential journal Philosophy and Rhetoric, and Perelman became established in the United States as a leading argumentation theorist.

He also made significant contributions to studies in law as director of the National Center for Research in Logic at the Université Libre de Bruxelles, and through continued publications on legal philosophy and argument.

[3] Perelman's friend, Mieczysław Maneli, wrote about his attitude towards Judaism: "He very consciously rejects any theology or earthly or heavenly salvation, any monism of values, any absolutistic interpretations of human needs and forms of freedoms.

After completing De la justice (in French), 1944, Perelman rejected the usefulness of logical positivism beyond its applications to pure science.

Because these approaches relied on a series of self-evident and mutually supporting axioms, any perceived error would disable the entire philosophy and its claims to reveal universal and absolute truths.

After encountering an excerpt of Brunetto Latini in the appendix of Jean Paulhan's Les fleurs de Tarbes (in French), Perelman began researching ancient Greco-Latin approaches to argumentation.

In the Topics and elsewhere, Aristotle opposes the demonstrative approach to dialectics, or rhetorical reasoning, which relies on premises that are acceptable in a given situation and are thus contingent.

For Perelman, then, a viable philosophy—capable of establishing aspects of being and inducing reasonable action—must be constructed according to probabilities and must be able to withstand impositions of value and other contingencies stemming from its reception by particular audiences.

To uncover the logic that governs these beliefs and ideas, Perelman and Olbrechts-Tyteca rely on a regressive philosophy that accounts for the variability of particular situations and particular values.

Following Frege's comprehensive approach to the study of mathematics, they collected a wide range of writing from academic, professional, religious, and popular realms to devise and apply their theory.

Perelman hypothesized that the rationale governing non-formal argument could be derived from the principles of rhetorical theory and from considerations of audience and values in particular.

Perelman, in contrast, believes not only that epideictic rhetoric warrants more attention, but that the values normally limited to that genre are in fact central to all argumentation.

"Epideictic oratory", Perelman argues, "has significance and importance for argumentation because it strengthens the disposition toward action by increasing adherence to the values it lauds" (1969, p. 50).

Definition is a common quasi-logical approach that is used not only for establishing the meaning of a term but also for emphasizing certain features of an object for persuasive purposes.

While these techniques appear to share the qualities of formal demonstrations, Perelman notes that for all quasi-logical approaches, "complementary, nonformal hypotheses are necessary to render the argument compelling" (2001, p. 1398).

Prominent criticisms by Jürgen Habermas, Henry Johnstone Jr., and John Ray challenge the practicality and applicability of Perelman's concept.

The work has been translated, in whole or in part, into nine languages and has been described variously as "groundbreaking", by J. Robert Cox, a "bombshell", by Michael Leff, and as "one of the most influential modern formulations of rhetorical theory", by Brian Vickers.

The new rhetoric and its later developments have been foundational for argumentation theory in the last thirty years, and Perelman's work has influenced studies ranging from justice and reason to social psychology and political geography.

[9] When abiding by the universal audience, it is difficult to construct a persuasive argument, as the speaker must use general and vague language to be cognizant of all the audience-members' values and ideals.

[11] While the concept of the universal audience has been criticized for trying to create complete agreement, Perelman claims its main purpose is to steer the speakers towards reasonableness.

The German philosopher Hans-Georg Gadamer cites Perelman's work on rhetoric as an influence on the hermeneutical philosophy he presented in Truth and Method, his masterpiece.