 For Hume all our simple ideas are derived from impressions (THN 1.2.3.2–3). Hume’s attacks on notions of substance, mode, essence, force, power, self, and—of course—God, all rely on his rhetorically powerful ability to ask to what impression such notions can be traced (e.g., THN 1.1.6; 1.2.5.28; 1.4.14, and 1.4.5.3–4; on idea of God, see EHU 2.6). For, “[I]deas always represent the objects or impressions, from which they are derived” (THN 1.2.3.11). In the scholarly literature, this has become known as the “copy principle” (Garrett 1997: chapter 2). If no such objects or impressions are to be found, then one must conclude that such ideas are the product of “passions and emotions” (THN 1.1.6.1), a “trivial suggestion of the fancy” (THN 1.4.7.6), or “some imperfection in [the] faculties [of mind]” (THN 1.1.7.8). The thrust of Hume’s account is to make talk of, say, substance or force (power, God, etc.) seem either meaningless or restricted to the particular qualities of bodies from which the idea is derived (THN 1.1.6.1; EHU 4.2.16). At best, they have reference to “an effect, or some other event constantly conjoined with” the cause (EHU 7.2.29; for a more detailed account, see the entry on Hume   ).  Thomas Reid, who saw what was at stake, described the strategy as “a tribunal of inquisition erected by certain modern philosophers before which every thing in nature must answer” (An Inquiry into the Human Mind: or the Principles of Common Sense, Chapter 6, Section VIII). 