 Hartley also agrees with Berkeley’s solution to this problem: we perceive a coherent world thanks to the generation of “ideas” (cognitive, semantic, and pragmatic responses to the world) through the “joint impression” of sensations from distinct sensory modalities—sight, hearing, and especially touch. As does Berkeley, Hartley identifies feeling or touch as “the fundamental source of information in respect of the essential properties of matter” and “our first and principle key to the knowledge of the external world” (OM 1, prop. 30). Thus, Hartley writes, “we call the touch the reality, light the representative.” The sense of sight “may be considered, agreeably to Bishop Berkeley’s remark, as a philosophical language for the ideas of feeling” (see Berkeley [1709] 1948, sections 6.4, 6.8, and 9.4).