It arranges all entities, structures, and processes in the universe, or in a certain field of study, into a hierarchy, typically based on how complex their organization is.
When arranged this way, each entity is three things at the same time: It is made up of parts from the previous level below.
The main levels usually acknowledged are those of matter, life, mind, and society.
Levels can be further analyzed into more specific layers, such as those of particles, atoms, molecules, and rocks forming the material stratum, or those of cells, organisms, populations, and ecosystems forming the life stratum.
Ideas connected to integrative levels can be found in the works of both materialist philosophers and anti-materialist ones.