Many instructional observation systems are designed to provide rough, qualitative, highly-evaluative assessments on numerous core dimensions of teaching. Such systems achieve comprehensive overviews of teaching but are poorly suited to answering many discovery-oriented research questions. In contrast, fine-grained agnostic systems are needed to pose and answer causal questions about instruction, and to fully understand instructional variation and change. More speculatively, I argue that the agnostic quality of fine-grained systems may also be useful in promoting teacher learning. Agnostic systems offer choice, withhold judgement, make room for locally-compensatory practices, and promote a greater locus of control. Instructional observation systems that carefully and agnostically quantify instructional processes may best help teachers leverage their professional judgment and invigorate their professional practice.