Merriam-Webster gives as one definition of competition (relating to business) as "[...] rivalry: such as [...] the effort of two or more parties acting independently to secure the business of a third party by offering the most favorable terms". Adam Smith in his 1776 book "The Wealth of Nations" and later economists described competition in general as allocating productive resources to their most highly valued uses and encouraging efficiency. Later microeconomic theory distinguished between perfect competition and imperfect competition, concluding that no system of resource allocation is more efficient than perfect competition. Competition, according to the theory, causes commercial firms to develop new products, services and technologies, which would give consumers greater selection and better products. The greater selection typically causes lower prices for the products, compared to what the price would be if there was no competition (monopoly) or little competition (oligopoly).