There are two senses in which words can be said to have meaning. There is the meaning which they have and which we know, when we use them correctly. In this sense most people who can use words with grammatical correctness would be said to know the meaning of the words they use. But there is another sense of the word meaning according to which most people would be said not to know the meaning of the words they are using. What most people habitually do, is to use words in a number of different meanings without realizing the fact.