  Into the late eighteenth century, we see Gassendi's influence in Reid's theory of external knowledge. This theory is centered on the notion of what he calls ‘suggestion’, or the evincing in us by our sensory data of concepts corresponding to the qualities of things in the world. In its broad sense, ‘suggestion’ consists in a signing relationship—as a matter of convention, custom, or biology—between things or events in the world which may be construed as signs (in the case of conventional signs, these may be linguistic or symbolic entities) and what those things or events signify. Here Reid draws on the long tradition of theories of signs, likely relying in this instance on Gassendi in particular, relative to the distinction between conventional (‘artificial’) and customary and biological (‘natural’).