Monopolies are large economic associations, such as cartels, syndicates, trusts, or concerns, which are owned by individuals, groups, or shareholders and which control industries, markets, or entire economies through a high concentration of capital and production. Their aim is to deny other producers the opportunity to compete. Their domination of the economy is the basis for their influence on all spheres of life. A monopoly may be granted by the state for certain purposes or may be acquired through the normal processes of business competition. In present day economics, a monopoly is presumed to exist when one firm has one third of the market, but the situation is considered to be more serious if three or four big firms have over half the market.