 Oresme’s discussion of the infinite in his Physics Commentary is another fascinating testimony to the originality of this outstanding medieval philosopher. Oresme demonstrates by thought experiments that of two actual infinites neither is bigger or smaller than the other. Oresme’s proof is somewhat reminiscent of Georg Cantor’s (1845–1918) demonstration that certain infinite sets are equinumerous. Thus Oresme shows by the principle of one-to-one correspondence that the collection of odd natural numbers is not smaller than the collection of natural numbers, because it is possible to count the odd natural numbers by the natural numbers (Sesiano 1996; Kirschner 1997, 79–83, 88–92).