Some minor revisions to the st paragraph of the Definition section   An obviously jumbled word somehow crept into the beginning of the nd sentence of the paragraph  The formula useoefficients of price elasticity  I put in a proposed revision    I also changed quantity to quantity demanded for the sake of clarity and completeness Its crucial that the definition be as precise as possible in emphasizing that PED is concerned only with changes in quantity demanded  Elasticity is one of the most difficult concepts in micro for most beginning students and for other potential readersusers  WPs customers they tend to get confused by the slightest ambiguity about which quantity we mean  An ounce of emphasis here doesnt preclude such confusion but it can help avoid a pound of it  In addition I added services to the definition as a token reminder that PED as well as the laws of supply and demand apply to both goods and services  The only other noteworthy revision was to the beginning of the last sentence in the first paragraph to place more emphasis on the PED for the most typical types of goods and services  Although the Giffen and Veblen exceptions are interesting they are almost negligibly rare anomalies compared to the overwhelming number of typical goods and services governed by the Law of Demand  Thats why it merits the rare status of a Law  The exceptions deserve discussion eventually in a later section but I think this introductory paragraph would be strengthened by giving them only the briefest possible mention in passing here  Instead this paragraph should focus attention on the crux of the issue that readers need to remember the takeaway namely  because the demand for most goods and services obeys the Law of Demand their PED coefficients will always be negative    Again elasticity is one of the most difficult topics at the introductory level of microeconomics  It doesnt serve this section or the article well to risk distracting students and other readers from the main point too early with such minor exceptions however interesting they may be to the intellectually curious readers Once weve made the main point as clear as possible then devoting some time to the exceptions is much less likely to cause confusion or ambiguity    I have one more suggested revision along this line for the paragraph and Ill return to it as soon as time permits  I made a few other copyedits were purely minor eg deleting an occasional unnecessary word to polish the prose just a bit