If you call a tail a leg, how many legs has a dog? Five? No, calling a tail a leg don't make it a leg. Is this really so? Imagine the whole English-speaking world and the people behind making leading English dictionaries gather up and collectively decide that from now on, the words 'tail' and 'leg' are synonyms. Would then the answer to the question 'how many legs does a dog have' be 'five'? What does modern philosophy of language have to say about this?