The search for patterns and attempts to describe relationships between phenomena are central to scientific activity. The hypothetical method relates observations by “inventing a fictitious substance or process or idea in terms of which the experiences can be expressed. The most important distinction between hypothetical constructs (of both types) and intervening variables lies in the predictive function of hypothetical constructs. It is usual for inferred constructs to start as relatively vague concepts associated with certain observations. The correspondence rules which tie an unobservable to observable events provide the general means for examining predictions from a construct. The claim that ‘schizophrenia’ is a scientific concept implies that it was derived from the observation of a pattern of regularities. The claim that the term refers to a syndrome implies that it was derived from, and now refers to, a particular type of pattern.