One of Parsons' concerns, within his general sociology, was to understand the relationship between social structures (how societies are institutionally organised) and social actions (the range of behavioural choices individuals believe are open to them). His basic argument, in common with all Structuralist sociology, is that the former condition the way the latter develop in society.
In this respect, Parsons used the concept of pattern variables to suggest that:
Different types of society (for example, pre-modern and modern) have
Different institutional relationships (for example, in pre-modern societies work is not clearly separated from family life, cultural institutions such as education and a mass media are not developed and so forth, and, therefore,
Different value-orientations (that is, the way people experience the social world significantly affects how they behave in that world).
Thus, Parsons argued that we could identify different patterns of behaviour, in different types of society, based on the different ways a society is socially (institutionally) structured. He termed these "pattern variables" for two reasons:
Firstly because they represent patterns of general values and
Secondly because they vary from society to society depending upon the relatively complexity of the institutional relationships in a society.
He argued there were, in relation to pre-modern and modern societies, two basic types of pattern variable:
Type "A" were considered to be characteristic of small-scale, pre-industrial, pre-modern societies, and
Type "B" were considered to be characteristic of large-scale, industrial, modern, societies.