Words express meanings or concepts. The concepts control the use of words through which we can communicate. Until recently, through thousands of philosophical tradition, words have been defined as singly, necessary and jointly sufficient conditions in various fields of studies such as philosophically oriented studies of language, linguistic studies psycholingustics, and psychological studies. In a word, words have been treated as necessity or essentialism. But beginning with Wittgenstein`s family resemblance theory("games"), various experiments of psychology proved that categorization is not yes/no problem but yes/no/not-sure problem, and thereafter a lot of studies showed that the classical view of concepts based on philosophy is a misconception or is strictly restricted to a few domains of vocabularies such as jargon vocabularies ("ketch"), kinship vocabularies ("bachelor"), and axiomatized systems ("triangle"). From this viewpoint, word meaning should be treated not as necessity but as possibility. This is the care of prototypical approach to word meaning. I have introduced two types of prototypical approaches in detail. Of course, prototypical approaches have some problems but they can solve seven problems which the classical view can`t. The essentials of prototypical approaches are as follows: (ⅰ) Category has central (typical, focal, core) members and peripheral members. (ⅱ) Category has internal structure in which prototype is the starting point around which peripheral members are clustered. (ⅲ) Theory of categorization: in order that 「A is B」 is true, every A shares at least one attribute with B or shares an attribute with some A` which shares an attribute with B. If we apply this prototypical approach to word meaning, we`ll find that a word has central and peripheral senses, that peripheral senses are clustered around prototypes (central senses), and that central and peripheral senses are connected by similarities. To know the meaning of a word means to know its prototypes. If knowing the meaning of a word involves knowing its defining conditions (necessary and sufficient), few of us, if any, can be said to know the meaning. Moreover we can`t remember all the senses of words because our memory is limited. we store the prototypes of a word in our memory and then give the same name to anything which has at least one attribute in common with the word. This prototypical approach makes us see the charge of word meaning in new ways. Though the change of meaning was focused on the figurative use of words in the past, ours is centered on similarity relations. In so far as any similarity between senses of a word is found, such a we doesn`t bring about the change of meaning. Therefore we dare to say that the figurative use of word can`t be regarded as the change of meaning because all the figuratives including metonymies and synecdoches use similarities.