This introductory chapter to the second book (“Some fundamental notions”) is short. It begins with Marshall’s plan to study “wants” (demand) in Book 3 and “efforts” (supply) in Book 4. Since these two are brought into equilibrium via money, or wealth, then Book 2 focuses on wealth.
§2. Marshall quotes Mill and Darwin to justify caution when considering the meaning of words and use of new words for old ideas (e.g., “interest” replacing “usury”). He says that older words might be more common but that newer words express recent ideas that are having a greater impact on society, since they are used to discuss important changes.
§3. The challenge, then, is to use common words in ways that the average person can understand, i.e., avoiding jargon. This pledge runs into trouble when one considers the many possible interpretations of a single word (“utility” springs to mind!)
§4. Thus it is important to use words that convey, rather than obscure, the results of analysis. I find this caveat to be wise and perhaps forgotten by too many modern economists who use “demand” when they mean “quantity demanded” or “elasticity” when they mean “price elasticity” — and that’s before even getting into our narrow definition of “elasticity,” which defies the normal use of the word!