Sentence:  Similarly, to take twenty-five years of free-form, cross-cutting social, political, economic, and historical writing growing out of work at a single, unstandard, American institution and isolate it as an "era" in such writing — a stage, a phase, a <WSD>line of thought</WSD> — is to pursue an agenda, take a position, state a case. 
Meaning of the word marked with <WSD> tags:  A specific way of thinking about a particular topic, concept, or problem.