(iii) Concerning the Weak Principle there has been an interesting development of a line of argument due to Black (1952) and Ayer (1954) in which it is proposed that there could be exact symmetry in the universe. In Black’s example it is suggested that there could be a universe containing nothing but two exactly resembling spheres. In such a completely symmetrical universe the two spheres would be indiscernible. Against this has been noted, e.g., Hacking (1975), that such a completely symmetrical