 Derk Pereboom (2011: ch. 5) identifies some candidates for physical quiddities in the history of philosophy. One comes from the Aristotelian tradition, on which matter is made up at least partly of prime matter. Prime materiality could be understood as a physical quiddity that underlies matter, which is structural. On Thomas Aquinas’s (1252–56) Aristotelian view, for instance, matter consists in extension in three dimensions, i.e., quantity. But quantity is a form, and in Aquinas’s view a form must inhere in something. That something, he thinks, is prime matter. Unlike quantity, prime materiality is not (in the terminology of  section 1.1)  a relatively intrinsic property of matter. Instead, it is an absolutely intrinsic property of matter, and it could be seen as a physical quiddity (Pereboom 2011: 85, 113). Admittedly, Aquinas held that prime matter is unintelligible. But other Aristotelians did not (Pasnau 2009).