Language is circular, pick up a dictionary and try this: look up a word, and then, look up a word in that definition [1]. Continue this process until you get back to the word where you started. Now sometimes this may happen very quickly. Sometimes, it may take a while to get there. Language depends on itself for it's own existence. It's a consensual hallucination perhaps. Because we all agree to believe that a certain word represents an object or a concept, then it does. Most of the time. Until of course, you run across someone who doesn't believe that the word means what everyone else does, and if they convince enough people that they are right, then they are. And the new meaning becomes "real."
[1] Related to this excercise is Hyperflow, an evolving hypertextual dictionary.