<p>The main goal of the paper is to provide the theoretical model for the a fortiori argument. After a brief history of a fortiori argument (especially in the works of Aristotle, Alexander, Cicero, and Boethius) we propose its general concept, components, and argumentation schemes, its classification, and finally, criteria for assessment. The main reason for this research is that this type of argument receives little attention in contemporary argumentation theory, and consequently critical thinking students have little knowledge of it, and yet, a fortiori arguments (or “arguments from the stronger”) are prevalent in both, academic and public, discourse. Therefore, the need to incorporate the concept of a fortiori argument into argumentation theory seems even more crucial. Additionally, we develop the diagrammatic method of assessing the inference in such arguments to finally present four critical questions needed for a critical evaluation of a fortiori argument.</p>