 The most influential attempt to analyse intrinsicality over the last 30 years has arguably been Lewis’s account of intrinsicality in terms of perfect naturalness. As Marshall 2012 explains, Lewis actually gave two importantly different accounts of intrinsicality in terms of perfect naturalness which philosophers often fail to distinguish: the first in Lewis 1983b, and the second in Lewis 1986a. Since the later Lewis 1986a account has been much more influential than the earlier Lewis 1983b account, we will restrict the following discussion to the later account. (For discussion of the earlier account, see Marshall 2012.)