The relative freedom and political stability of seventeenth- and eighteenth-century Britain produced an intellectual milieu amenable to advances in the natural sciences and philosophy. The major theme of British psychological thought was empirical, emphasizing knowledge acquired through sensation. The mechanism of this acquisition process was association. Founded by Hobbes but fully articulated by Locke, British empiricism retained the necessity of the mind construct while underlining the importance of sensations. Berkeley, Hume, and Hartley evolved skeptical positions concerning the reality of matter and mind that could have left the British movement in the same sterile position as French sensationalism. In addition, James Mill, although he was somewhat salvaged by the utilitarian influence, reduced associations to mental compounding. However, the Scottish common sense writers succeeded in restoring empiricism to a more flexible and open-ended position that recognized complex and integrative psychological phenomena. Thus, the later empiricism of John Stuart Mill, while adhering to scientific inductive methods, adopted a broadly based model of psychology that viewed mental operations and physiological processes as complementary and necessary dimensions of psychological inquiry. By the nineteenth century British philosophy was providing strong support for the study of psychology.

This chapter assesses five strategies that contractualist thinkers have put forward to conceptualize PSID as active participants to the social contract. These focus on (1) PSID’s talents; (2) their capacity to have a conception of the good; (3) their ability to engage with others or play a part in society; (4) their potential to develop (further) contractual capacities; and (5) their need for assistance by ‘collaborators’ or ‘cognitive prostheses’ in the nurturing and exercising of these capacities. These strategies attempt to ‘normalize’ PSID by modifying the benchmark requirements for counting as a contractor; or by arguing that PSID do meet these requirements, despite appearances to the contrary. While they are promising in terms of its application to less seriously disabled individuals, I find that social support, including ‘mental prostheses,’ is not a plausible solution for many profoundly disabled individuals, unless this support is conceptualized in a way that alters it beyond recognition or takes it beyond the autonomy-based contractualist paradigm to which it purports to be attached.