Professional historians would bring to bear a number of concepts to their view of legal departments. Below are several that they would apply.
Causality – does circumstance A lead to circumstance B (See my post of Jan. 25, 2008: causality with 10 references; and Jan. 25, 2008: over-determined events.).
Historicity – the importance of seeing the world as the participants at the time saw it, avoiding anachronisms (See my post of Oct. 24, 2008: historical references to management of legal departments with 7 references; and June 13, 2006: a historical lexicon of law department management terms.).
Primary sources – gathering facts and material for interpretation from the documents of the day
Ideology – realizing that even historians see “facts” through a prism of their beliefs (See my post of June 10, 2007: facts and theory intertwine; Jan. 15, 2007 #4: Whig history; and Sept. 22, 2008: a teleology of progress.).
Multiple disciplines – drawing on many sources, other than documents, to develop their understanding of the past (See my post of May 16, 2007: multidisciplinary views of law department management.).