Final answer:
Three incentives offered by groups to attract membership include purposive incentives (e.g., supporting the ACLU for civil liberties), solidary incentives (e.g., socializing with like-minded individuals in the Union of Concerned Scientists), and material incentives (e.g., discounts and services provided by AARP).
Step-by-step explanation:
Interest groups offer various incentives to attract and retain members, solve collective action problems, and advance their causes. Three common types of incentives include purposive incentives, solidary incentives, and material incentives. An example of a purposive incentive is when individuals join the American Civil Liberties Union (ACLU) to support civil liberties and constitutional rights. Solidary incentives are found in groups such as the Union of Concerned Scientists, where the reward comes from collaborating and socializing with like-minded individuals. Material incentives are given by organizations such as AARP, which offers tangible benefits like health insurance and discounts on various services for a nominal membership fee.