Empirical studies of technical and therapist variables in treatment cannot yield valid generalizations because of the uniqueness of each case. Professional practice must, instead, be seen as an application of a psychological “calculus”, which follows logically from definitions of given concepts. Seven necessary rules are suggested for psychological treatment: 1. Regard the client‐in‐her/his‐surroundings‐system (cs‐system) as your unit of reference and get to know this system. 2. Tolerate initial ambiguity and do not generalize from other persons in other life situations. 3. In matters relevant for treatment, do not objectivize, i.e. pronounce something to be true or false, good or bad, right or wrong, but always subjectivize, i.e. emphasize that FOR P something is true or false, etc. 4. Maintain your independence relative to the cs‐system you work with. 5. Understand the persons in the cs‐system. 6. Respect the persons in the cs‐system. 7. Care for the perso