As political control becomes more intense, intellectual liberties may be curtailed by censorship and the banning of meetings, books and the right of association. Conflicting group interests may result in tyranny by either the majority or a minority. Moral and religious freedom may be inhibited by law or by social taboo. Freedom of movement and employment will be reduced and the ability to make the best use of available opportunities will be inhibited by unequal distribution of state services, education, health, housing. Freedom of ownership and the freedom to do as one chooses with one's possessions will be restricted according to the prevailing ideology concerning materials and resources and the interaction of materials and resources, such as the air polluting effect of car exhaust fumes. Extreme forms of the negation of liberty include slavery, concubinage, and legalized discrimination such as apartheid.