Every word refers to a concept, which exists in the memory of the listener's mind.
Some concepts are the product of nonverbal experiences. Since the particular animals we saw differed from those seen by other people, our concept is slightly different from the concepts that other people have. On the other hand, certain concepts are the result of verbal or written explanations by other people. Here the explanations differed, so again our concept is not identical to that of other people. Any concept we have, therefore, consists of other, previously learned, concepts and these concepts differ from person to person.