Philosophers, mathematicians, and other ancient and modern thinkers, such as Aristotle, Plato, Frege, Wittgenstein, and Russell, have made a distinction between thought corresponding to reality, coherent abstractions (thoughts of things that are imaginable but not real), and that which cannot even be rationally thought.
-- wikipedia
So basically this is the same thing as "If a tree falls in the forest and no one is around to hear it, does it make a sound?" Or even the age old question "which came first the chicken or the egg?"