Nominalist: Every Jew defines Judaism. Judaism is thus the sum of the attitudes and beliefs of all the members of an ethnic group. Each member of the group serves equally well to define Judaism.
Harmonistic: The common denominator among the sum of all Judaisms. All Jewish data, writings, and other records together tell us about a single Judaism, which is defined by the least common denominator among all the data.
Theological: The study of Judaism by studying the theological ideas of the various texts. This provides a well drafted description, but ignores all the questions of context and social relevance. Its Judaism came into existence for reasons we can not say and addressed no issues faced by ordinary people, and constituted a set of disembodied, socially irrelevant ideas that lack history and consequences. So it can be described and analyzed but not interpreted.
Historical: The working through sources in the order in which it is assumed that they reached closure, so as to find the order and sequence in which ideas came to expression. Each document is studied as a Judaism before comparing and contrasting can be done.