Evaluation can be considered as a general activity not specifically confined to educational settings. This paper considers the assumptions leading up to a definition of value, defines value within the framework of the stated assumptions, and discusses evaluation as a conceptual, rationalizing activity. Terms defined in the paper's first section include infinite regress, distinction, potential set, variety, constraint, decision, conflict of interest, and value. An evaluation model is developed which regards the matching of concepts and world states as the key feature of evaluation. Section 2 of the paper draws implications from the general evaluation model for the specific role of the educational evaluator. Section 3 considers the training needed by an evaluator if the general model is accepted. (Author)