This chapter introduces foundational psychological theories of basic emotions and examines their relevance for the study of emotional appeals in argumentation. It begins by outlining two dominant approaches: the dimensional model, which conceptualizes emotions along continuous scales of valence and arousal, and the categorical model, which identifies distinct basic emotions such as anger, fear, sadness, joy, and disgust. Special attention is given to the theories of Ekman and Plutchik, whose models emphasize stimulus-response structures, automatic appraisal, and adaptive behavioral functions. These models are presented not as comprehensive accounts of emotional life but as simplified, intersubjective frameworks useful for operationalizing emotional appeals in discourse. The chapter distinguishes between emotions expressed by speakers and emotions elicited in audiences, arguing that the latter are especially relevant for understanding pathos in natural language argumentation. By viewing emotion-eliciting language and argument schemes as stimuli that activate fast, affective responses, the chapter offers a psychological foundation for the interactional model of pathos developed throughout the book. This framework prepares the ground for the computational tools and empirical studies that follow.