Downward entailing quantifiers are more difficult to process than upward
entailing ones. What cognitive processes cause this monotonicity effect is,
however, a matter of current debate. We test predictions about the
underlying processes that are derived from two broad classes of competing
theoretical proposals: two-step and pragmatic processing models. To this
end, we model data from two web-based verification experiments, in
particular, reaction times and accuracy, using the diffusion decision
model. Our results support both two-step and pragmatic processing models
and indicate two separate sources of the monotonicity effect that map onto
different DDM parameters.