Facet theory derives from the work of Louis Guttman, whose early research was concerned with developing scales but was troubled by defining their content. It was his conviction that behavioural research dealing with complex issues should proceed logically by conceptualizing and defining in substantive terms what is being studied before proceeding with data collection. Facets and their constituent elements are ways of classifying variables and are formally laid out in a mapping sentence. The mapping sentence indicates the role that the facet is hypothesized to play, which in turn is based on the rationale. A structure frequently reported in the research literature is a radex, which comprises facets playing a modulating role combined with a polar role. An important goal of facet theory is to identify and establish recurring patterns and regularities. Through replication and confirmation, such recurring findings may lead to the ultimate goal of establishing laws of behaviour.