There are certain laws that govern this universe of ours. for example - the universal law of gravitation, the maxwell's laws and in case it does exist, the TOE... Now consider a universe as a set of laws. So if we give any random set of laws, it uniquely defines a universe. There can of course be some constraints on the set of laws in order to make it define a possible universe, for example, one of the constraints might well be that none of the laws in the set should contradict another. Once we define a universe in this way, we can start imagining various kinds of bizarre universes with several unimaginable laws. And this exercise raises an interesting question. Is there a law that MUST be true in all kind of universes? And if you think on this question for a while, you might come up with the following law :- Consider an object which is very rigorously defined, for example, may be, a red ball (a red ball might not be rigorously definable, but that's not the issue here... let's just assume that it is). So then in a given universe, a red ball either exists or doesn't exist. Now let's analyse this law. Of course, in our universe, it is true... a red ball either exists or doesnt... But is it necessarily going to be true in all the conceivable universes? I mean, are logical statements like this bound to be true in ALL the universes we can possibly imagine?