People's representations of most and arguably all linguistic and non-linguistic categories are probabilistic. However, in linguistic theory, quantifier meanings have traditionally been defined set-theoretically in terms of categorical evaluation functions. In 4 ``adaptation'' experiments, we provide evidence for the alternative hypothesis that quantifiers are represented as probability distributions over scales (e.g., Zadeh, 1965). We manipulate exposure to different distributions of ``some'' and ``many'' and find that listeners adapt to those distributions, as predicted. Our results suggest that the interpretation of quantifiers is best modeled as a process involving rich, probabilistic representations.