Aristotelian electrodynamics (AE) describes the regime of a plasma with a very strong electric field that is not shorted out, with charge current determined completely by pair production and the balance of Lorentz 4-force against curvature radiation reaction. Here it is shown how the principal null directions and associated eigenvalues of the field tensor govern AE, and how force-free electrodynamics arises smoothly from AE when the eigenvalues (and therefore the electric field in some frame) vanish. A criterion for validity of AE is proposed in terms of a pair of "field curvature scalars" formed from the first derivative of the principal null directions.

5 pages; v2: several small changes to the manuscript to improve clarity of explanations; removed condition on radius of curvature of field lines for applicability of force-free approximation; nearly matches version published in PRD