Do we need definitions?

      Question:   Some would argue that certain concepts, or objects, do not require definitions because they have certain known characteristics that distinguish them from other things. For example, we know the characteristics of a cat; therefore we no longer need a definition for it. However, wouldn't definitions be necessary when it comes to teaching and/or learning a new language, especially if the concept is specific to one culture, and therefore does not have an equivalent in any other languages?

      I have concluded that yes, definitions would be necessary in this situation because if teaching someone a new language, we would need to describe the characteristics of new words, therefore defining them. By describing the characteristics of the new word, we are giving a definition, whether or not it is exactly the same definition that would be found in a dictionary. Definitions just list the characteristics of the word, or the necessary and sufficient properties that something needs to have in order to be called that word. 

      If we didn't have definitions, listing necessary and sufficient characteristics, we wouldn't be able to discriminate between different objects. For example, if we didn't have a definition for the word cat, we wouldn't be able to discriminate between what is and what is not a cat. People could start claiming that dogs are cats, and it would be justifiable because there is no definition to act as a reference. We also need these definitions to be specific enough to make sure that things that do not belong are not being included in the definition. For example, if the definition for a cat was, "an animal with four legs, eyes, ears, a nose, a mouth, and a tail," then we could claim that many reptiles are cats because they meet these characteristics. Therefore, not only do we need definitions, but these definitions must also list necessary and sufficient characteristics that are specific enough to exclude any objects that do not adequately fit the term.