From the ancient time, philosophers in west and east and also linguists dealt with nonexistent words. The main question always was this that how we can understand words such as ''Rostam'' which don't refer to anything in the physical word and even uses it in different sentences in different combinations. Different answers are proposed by philosophers to this question. In a way that each has focused on one aspect. In this article it is tried that by semantic means a response for this problem provided and some criteria for their classification as the first way of knowledge are provided.
