  His own approach to signs is evident in his speculation, undertaken at the urging of Darwin, about the origin of self-consciousness. Here Wright treated concepts as images. He traced the emergence of self-consciousness in terms of human awareness of different kinds of signs (usually vocal, he said) that recall images in thought. The images themselves act as signs when a human being reasons, but “with reference to the more vivid outward signs, they are, in the animal mind, merged in the things signified, like stars in the light of the sun” (PD 209). The conscious awareness of the difference between outward and inward signs is crucial to human awareness, he believed. This awareness may have come with the “consciousness of simultaneous internal and external suggestion” and the recognition of the outward sign as a substitute for the inward sign (PD 210). The key to rationality is the outward sign itself, i.e., elements of language, being made the object of attention (PD  206).[9]