Structural Functionalism - How each part of society functions together to contribute to the whole.
Conflict Theory - How inequalities contribute to social differences and perpetuate differences in power.
Symbolic Interactionism - One to one interactions and communications.
Figuration - The process of simultaneously analyzing the behavior of an individual and the society that shapes the behavior.
Sociological Imagination - The ability to understand how your own past relates to that of other people, as well as to history in general and societal structures in particular.
Moreover, Gibbon carefully studied and compared all the primary sources, and it may be urged that he has given a truer, fuller, and more attractive account of the period than can be found in any one of them. His Decline and Fall of the Roman Empire is certainly a work of the highest rank; but, nevertheless, it is only report of others' reports. It is therefore not a primary but a secondary source.
A secondary source is one based on other sources.