 The second reflection concerns the “capitol part” sensations bear in the “notion we form of the [object perceived]” (Reid 1785 [2002: 204]). Unlike the easily forgotten sensations that accompany perception of PQs, many sensations caused by SQs have a salience that makes us attend to them and form concepts of them. They are not just signs of the qualities when we perceive them: “the thought of a secondary quality always carries us back to the sensation it produces”, This is because although each perception is conjoined with a sensation proper to it (Reid 1785 [2002: 199]), relative notions specify every object as an unknown cause. We have only their known effects by which to reflect on them and mark them as different from each other. This has been called the “capitol part” thesis. In effect, post-perceptual apprehension of SQs is mediated by conception of the sensation that is its sign—apparently, a mediation Reid considers innocuous (see Reid 1785 [2002: 134]; for different views about what that might be, see Nichols 2007: ch. 10; Copenhaver 2004; Buras 2011; Van Cleve 2015: 297–300). The implications of this for the meanings of SQ terms is disputed by scholars.