Where q> E 4>10 i.e. where q> is a one-place predicate, OJtp is called a property. Note that this is the ~ide logician's use of 'property' in which, say, standing three hundred yards from the biggest wooden building in the world is a property; viz., the operation OJ such that for any a E D, OJ(a) is the proposition that a is standing three hundred yards from the biggest wooden building in the world. (And remember that this proposition is the set of those and only those worlds in which a is standing three hundred yards from the biggest wooden building in the world.) Many philosophers would be unhappy with this as a property since the construction of another wooden building taller than the one a is standing three hundred yards from seems an odd way to effect a change in a's properties. I have no wish to defend either the wide or the narrow use of the word 'property' but simply state how it is being used in this book. Where OJ is an n-place operation from Dn to r?J>W we shall sometimes speak of it, by extension, as an n-place property, though the word 'relation' would probably be more correct in such cases.