Phenomenalism, instrumentalism, and realism may be used to describe the denotation (or ontology) of educational terms. Phenomenalists argue that terms can be translated into expressions in an observation language. Instrumentalists maintain that terms are tools that are useful in explanations and predictions. Realists believe that terms denote entities that exist in the external world. The "appropriateness" of each ontological position is examined by the author, depending on: a) whether the term in question does not or does imply a prediction; b) whether the prediction is or is not based on a postulated causal mechanism; c) if not based on a causal mechanism, whether the term is used in prectical decision making or in theory construction.