An ontological primitive is a concept that is so basic that it cannot be further reduced or divided into constituent parts. As proposed by the philosopher Iain McGilchrist, it refers to a fundamental unit or element of being that cannot be broken down or explained further. Ontological primitives form the foundation of being and must be experienced in order to be understood; they cannot be understood through rational analysis alone. They provide the basic categories of understanding and form the building blocks of reality as we experience it.

See also: right hemisphere, left hemisphere, hemispheric hypothesis, corpus callosum