A popular form of monism is materialism, in which everything is considered to be made up of matter that is expected to behave in certain ways. Such a materialism usually denies reality to spiritual ideas or entities, and also frequently involves some form of reduction, in which complex phenomena are held to be ultimately explainable in terms of the operations of fundamental units of matter. The parts would thus be expendable, and replaceable, something it is supposed that components of the biosphere are not. Materialism, just described, is not the only form of monism. This form of monism denies ultimate existence to changing phenomenal existence.
Dualism holds that there are two fundamental substances.
This is a very ancient and popular way of seeing the world that can account for a perfect god and an imperfect world. Environmentalists often object to dualism because it forces a separation between humans, as mental or divine beings, and nature, as material existence. This term encompasses a variety of related concepts, some valued in Western culture, some castigated.