Poortman was the maker of the Repertory of Dutch philosophers,
Repertorium der Nederlandse Wijsbegeerte, which can be consulted on line at the site of the Leiden University.
He formulated the idea of a hylic
pluralism (in Dutch hylisch pluralisme) of the plurality of matter, a model of the universe in which science and metaphysics are no longer contradictory. This vision was explained in his four volume work, Vehicles of Consciousness.
Poortmans categories
Poortman distinguished six different
metaphysical views of the world, which he named from Alpha to Zeta.
Beta: the view that only
matter exists, but that there are different kinds of matter (hylic pluralism), specifically that
God and other spiritual beings are created of a finer kind of matter, not visible to our scientific instruments.
Gamma: that only matter exists, with the exception of one single entity which is not material. This entity may be
God,
Brahman, etc. This is the view held by Poortman himself.
Delta: the view that two separate kinds of material and one kind of spiritual, immaterial entity exists, for example the early Christian and
Gnostic belief that man was made of
body,
soul and
spirit, where the first two are different forms of matter and the spirit is immaterial.
Epsilon: a view in which matter and mind are totally separate things. This view was for example held by
René Descartes in his cogito ergo sum statement, see
mind dualism.
Zeta: monistic idealism or illusionism, where matter is seen as some kind of
emanation of God or another spiritual being. Especially this classification applies to the
Brahman of the
Hinduism.
References
J. J. Poortman: Vehicles of Consciousness. The Concept of Hylic Pluralism (Ochema), vol I–IV, The Theosophical Society in Netherlands, 1978