The Introduction outlines the key differences between the traditional use of propositional logic in psychotherapy and modal logic as the logical foundation of Modal Integrative Psychotherapy. One of the main differences between the two is that, while the emphasis of traditional psychotherapy is on changing the client (thus the subjective experience of the world), modal logic (and, correspondingly, Modal Integrative Psychotherapy) ventures into seeking to change the modal worlds, or “possible worlds” as sets of circumstances outside the person that determine the person’s experience of reality. This introduction points at the role of sociality as a normative foundation of our perceptions and self-perceptions and sets the stage for a fuller discussion of key elements of modality in the theory, interventions, and overall methodology of Modal Integrative Psychotherapy.