  “A line is something in a body. And what it is it owes to the body. That is, it keeps its being through the body. This is explained as follows. If it is separated from the body, it does not subsist. Who by any sense faculty ever grasped a line separated from a body?” [Boethius, Second Commentary on Porphyry's Isagoge I, xi, 14–21 (English translation  from Spade 1994: 23–24)]