After more than a century of work in the field a wealth of archaeological material has been recovered for analysis and interpretation by the prehistorian in his continuous attempt to understand the cultural traditions and relationships of his own ancestors. A varied array of analytical methods have grown to aid him in his task of defining ancient cultural groups. In many cases these methods have grown without their underlying principles being perfectly understood or clearly stated: they were used first and understood later. A typical example of this process has been the changing implications of the ‘Three Age System’. Curiously the position often taken today seems to suggest that no principles underlie the study of prehistory, since when these are defined they are never used and those used are rarely defined. This position is contrary to the observations of Social Anthropology and Ethnology and the pioneer work of the late Professor Childe. Wherever human actions or their fossil results, the artefact, can be studied they show distinctly non-random action conditioned by the peculiarly human attributes, namely foresight and transmitted culture. In other words they obey certain limiting principles. The present position in the study of prehistory is similar in many ways to the position of the emergent Natural Sciences in the 17th and 18th centuries; data has been amassed, but the principles remain dimly perceived or are even denied existence.