 Like gravitational attraction, the associative principles are original, and so can’t be explained further. Although the associative principles’ “effects are everywhere conspicuous” their causes “are mostly unknown, and must be resolv’d into original qualities of human nature, which I pretend not to explain”. Accordingly, we should curb any “intemperate desire” to account further for them, for doing so would take us illegitimately beyond the bounds of experience (T 1.1.4.6/12–13).