The concept of 'operational' in this context implies that a statement or formulation must be to some extent confirmable, at least in principle, and must be related to observable data. Analytic principles can be scientifically and legitimately formulated in terms of hypothetical constructs, but these principles can be presented so that they become more easily empirically confirmable, clearer, less tautological, and more practical. Ellis offers a basic operational vocabulary enabling him to restate, in operational terms, some of the main hypotheses of Freud's An Outline of Psychoanalysis. The key words used in operational definitions are anchored in human perception and response, and it is shown how those hypotheses may be confirmed or disproved by clinical or experimental observation.