 The kind of unity which the pantheist thinks to find in nature can vary from a very strong metaphysical oneness, like that of Parmenides, which excludes all diversity or difference, to a much looser systematic complex of distinct but inter-related elements, but the four species of unity most commonly defended are: (1) the unity of all that falls within the spatio-temporal continuum under a common set of physical laws, (2) the reductive unity of a single material out of which all objects are made and within which no non-arbitrary divisions can be made, (3) the unity of a living organism, or (4) the more psychological unity of a spirit, mind or person.