It may be true that defining key terms and concepts is important to the start of any productive argument, but not all definitions are the same. Most logic texts list five different types of definitions which people might use. This can give the impression that the matter is pretty well settled, but its not. In fact, the assumption that the matter is settled is part of what gives rise to debates about the nature of definitions every so often. It might seem strange that a lot of ink and time is spent on something so basic a a definition, but sometimes it is the most basic of concepts that are the most problematic.
Why is discussing the nature of definitions important? If two people involved in a debate are using entirely different types of definitions for the same term, they may only end up talking past each other. Definitions shouldnt necessarily be accepted at face value, but analyzing the worth of a definition requires understanding what sort of definition you are faced with.
What is a definition? In all cases, a definition is any group of words or symbols designed to explain the meaning of some other word or symbol. Good definitions are those which advance communication and understanding, while bad definitions are those which hinder or at least fail to advance communication or understanding. Even a bad definition is still a definition, and over the course of debates you may find more bad definitions than good ones.
All definitions are made up of two parts, the definiendum and the definiens. The definiendum is whatever word, symbol, or group of words is being defined; the defiens, then, is whatever words are being used to do the defining. Thus, in the statement a definition is a group of words or symbols designed to explain the meaning of some other word or symbol, the definiendum is a definition and the definiens is everything else.
Do definitions convey information? Thats a matter of some debate. There are philosophers who argue that because a definition is simply a way of stating that the words in the definiens can be replaced by the words in the definiendum, nothing new is learned. Others, however, argue that because definitions help us clarify and explain ideas, they can therefore help us reveal deeper philosophical truths about the nature of not only language, but our own concepts and thoughts.
What separates a good from a bad definition? Thats a difficult question to answer, but a general principle to keep in mind is that it depends a great deal on context specifically, what the purpose of the definition is. To answer is this a good or a bad definition, one must first answer what are we trying to achieve with this definition? Thus we must examine the specific situation in which the definition is given and what sort of definition it is supposed to be.
Lets take a look at the five different kinds of definitions you may encounter and how to approach them: