The research literature contains disagreements about the meanings of the terms proposition and hypothesis. We define a proposition as a statement about concepts that may be judged as true or false if it refers to observable phenomena. When a proposition is formulated for empirical testing, we call it a hypothesis. As a declarative statement, a hypothesis is of a tentative and conjectural nature.

Hypotheses have also been described as statements in which we assign variables to cases. A case is defined in this sense as the entity or thing the hypothesis talks about. The variable is the characteristic, trait, or attribute that, in the hypothesis, is imputed to the case. For example, we might form the hypothesis, “Executive Jones (case) has a higher than average achievement motivation (variable).” If our hypothesis was based on more than one case, it would be a generalization. For example, “Executives in Company Z (cases) have a higher than average achievement motivation (variable).” Both of these hypotheses are examples of descriptive hypotheses.