The field dependence of blocking temperature TB and the temperature dependence of coercive force Hc are shown to be analogous functions. Coercive force data, obtained routinely with standard equipment, can therefore be used in analog tests of theories of thermoremanent magnetization (TRM). Analog Hc data reported in this paper for single-domain and small multidomain magnetite dispersions and a variety of rocks are matched equally well by N¿el's (1949) theory of thermally activated magnetization changes or N¿el's (1955) theory of field-induced domain wall displacements. The temperature dependence of domain wall pinning is a crucial unknown in the wall displacement model, allowing considerable latitude in curve fitting. If the thermal activation model is assumed, reasonable values are found for the volume activated in a single magnetization reversal or wall jump in the fine- and medium-grained rocks tested. Additional independent evidence from hysteresis and microscopic examination is necessary, however, to choose between the competing TRM models in individual cases.