With an individual with good practical knowledge as the participant, we aimed to identify practical knowledge of psychotherapy for people with intellectual disabilities through dialogues with deep commitment with researchers including aspects of tacit knowledge. Researchers were also therapists, and this study was an attempt at generatively transmitting tacit knowledge between generations. We identified the structure of the practical knowledge consisting of three layers. Psychotherapy is considered a process that leads to “understanding and sharing” after identifying “the language” as a collaborative medium that allows clients, who “do not understand” their own “subjective world,” to connect with the subjective world and share with others. Based on this understanding, psychotherapy for individuals with intellectual disabilities is considered as a practice of separating difficulties with “understanding” from clients and recovering the commonality of an act of “understanding.” Psychotherapy that aims to achieve “understanding and sharing” is an act of therapists transmitting (inheriting) tacit knowledge to live in one’s own way to their clients, identifying the similar structure to the result and methodology in this study.
