 That sensations and perceptions of the qualities that cause them are distinct mental acts is, like the theory of ideas, a point on which philosophical theories of perception founder as Reid sees it (e.g., Reid 1785 [2002:199–200]). His empirical evidence shows that sensations and the corresponding qualities have the same names in virtually all human languages: “smell of a rose” is ambiguous as between an aromatic feeling and a quality possessed by a kind of flower. The quality and the sensation are generally confounded by imagination as if they were the same operation (Reid 1764 [1997: 43]; 1785 [2002: 193–99]). This is benign for ordinary purposes, according to Reid, but a thorn in the side of philosophers. It obscures a difference among the various qualities perceived by sense that Reid’s decisive division of sensation and perception brings to light.