The introduction of the psychophysical technique of magnitude estimation to the study of acceptability judgments (Bard et al. 1996) has led to a surge of interest in formal acceptability-judgment experiments over the past fifteen years. One of the primary reasons for its popularity is that it was developed as a tool to measure actual units of perception, offering the possibility of data that is inherently more informative than previous scaling tasks. However, there are several untested cognitive assumptions that must hold in order for ME to be the perceptual measurement test that it is purported to be. Building on the recent formalization of these assumptions in the psychophysics literature (Narens 1996, Luce 2002), this article presents two experiments designed to test whether these assumptions hold for acceptability-judgment experiments. The results suggest that the cognitive assumptions of magnitude estimation do not hold for participants in acceptability-judgment experiments, eliminating any reason to believe that ME could deliver inherently more meaningful data than other acceptability-judgment tasks.