This chapter examines some aspects of the influence of the Sorites Paradox in psychology. The first section starts out with a brief discussion of the analysis of slippery slope arguments in the psychology of reasoning, to introduce the relevance of probabilistic considerations in that domain. We then devote most of this chapter to the analysis in psychophysics and in the psychology of concepts of the complex relationship between discrimination and categorisation for items that differ very little. The second section emphasises the centrality of probabilistic modelling to represent the way in which small differences between stimuli affect decisions of membership under a common category. The third section focuses on experimental data concerning unordered transitions between prototypes, then the final section looks at data concerning ordered transitions between prototypes (dynamic Sorites).

Contextualist accounts of the Sorites Paradox are sometimes taken as claiming that vagueness just is (a form of) context-sensitivity, and that the paradox is solvable by appeal to that context-sensitivity alone.We argue that this interpretation is misleading.Certainly contextualist accounts often provide plausible diagnoses of the intuitive pull of the soritical premise, and, due to their dynamical nature, they are well-suited to explain linguistic behaviour in so-called forced-march versions of the puzzle.However, they usually have to be coupled with non-contextualist accounts in order to resolve the paradox proper.We begin by distinguishing various contextualist explanations of the appeal of the soritical premise.Then we point out three main virtues of these approaches and discusssome objections.Lastly we consider the prospects for a recent descendant of contextualism that is meant to solve the paradox proper as well as the forced march puzzle.