As a teacher of the New South Wales Higher School Certificate Geography Syllabus in the 1970s, I became aware of problems of interpretation and implementation of syllabus documents dealing with models and theories of human aggregate behaviour. A positivistic underpinning allowed explanation in human geography to employ deductive - nomological methodology. This field study investigates a defined literature of academic geography including journals, and both secondary and tertiary documents to identify the extent and quality of nomothetic and idiographic traditions from the late 19th century to the mid 1970s. The literature prior to the late 1950s revealed a dominant regional tradition and idiographic methodology with an emphasis on description of uniqueness of areal phenomena. But underlying currents of a nomothetic nature, running parallel to this regionalidiographic tradition,exerted a noticeable challenge to gain acceptance in geographic circles. This kind of nomothetism was in the form of environmental determinism which held that physical laws operating in nature were also at work to shape and direct human societies. Environmental determinism contained generalised assertions, enjoyed some appeal, but lacked rigorous justification. Even within regional frameworks, authors used environmentally induced determinants to explain the unique character of regions. Not until the 1930s did environmental determinism lose its appeal, after which time the regional - idiographic tradition strengthened as an explanatory mode of human behaviour. Nomothetism emerged in the late 1950s in Australia in the application of models and theories explaining human behaviour. Normative theory was supported by an increased use of quantification and by the growing preference for systematic studies in geography. Neither mode of explanation exists at the total exclusion of the other; so that while nomothetism enjoyed widespread appeal in academic geography from the late 1950s, significant challenges were mounted against it because of its inadequacies as a mode of explaining human aggregate behaviour. Nomothetic explanation in human geography can be seen at the research level and in education circles. Many normative models and theories found their way into senior geography courses to the extent they promoted a systems approach. Teachers would have been aware of normative theory in geography from their university studies and teacher training courses during the late 1950s and throughout the 1960s. The tension between associated explanatory modes in systematic and regional geography becomes apparent in the analysis of the N.S.W. H.S.C. Geography Syllabus in which confusing statements raise problems for teachers interpreting and implementing this prescriptive document. Given these tensions and problems of explanation in human geography, the adoption of a critical rationalist viewpoint as propounded by Karl Popper is suggested as a possible solution for geography teachers when interpreting a syllabus such as that of the N.S.W. H.S.C. Falsification rather than verification should be the node of inquiry towards explanation of human aggregate behaviour.