who gave the concept of elasticity of demand
Price elasticity of demand Together with the concept of an economic "elasticity" coefficient, Alfred Marshall is credited with defining PED ("elasticity of demand") in his book Principles of Economics, published in 1890.[20] He described it thus: "And we may say generally:â€” the elasticity (or responsiveness) of demand in a market is great or small according as the amount demanded increases much or little for a given fall in price, and diminishes much or little for a given rise in price".[21] He reasons this since "the only universal law as to a person's desire for a commodity is that it diminishes... but this diminution may be slow or rapid. If it is slow... a small fall in price will cause a comparatively large increase in his purchases. But if it is rapid, a small fall in price will cause only a very small increase in his purchases. In the former case... the elasticity of his wants, we may say, is great. In the latter case... the elasticity of his demand is small."[22] Mathematically, the Marshallian PED was based on a point-price definition, using differential calculus to calculate elasticities.[23]
Monopolistic competition Monopolistic competition is a type of imperfect competition such that many producers sell products that are differentiated from one another (e.g. by branding or quality) and hence are not perfect substitutes. In monopolistic competition, a firm takes the prices charged by its rivals as given and ignores the impact of its own prices on the prices of other firms.[1][2] In the presence of coercive government, monopolistic competition will fall into government-granted monopoly. Unlike perfect competition, the firm maintains spare capacity. Models of monopolistic competition are often used to model industries. Textbook examples of industries with market structures similar to monopolistic competition include restaurants, cereal, clothing, shoes, and service industries in large cities. The "founding father" of the theory of monopolistic competition is Edward Hastings Chamberlin, who wrote a pioneering book on the subject, Theory of Monopolistic Competition (1933).[3] Joan Robinson published a book The Economics of Imperfect Competition with a comparable theme of distinguishing perfect from imperfect competition.