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Part / part concept / ontology / Meixner: no category but transcendental - therefore there are different mereologies (doctrines of the part) for matters, for individuals, for properties.
Part / constituent / Meixner: individuals can only be constituents of individuals if they are also parts of them - so in another possible word there are only counterparts of us - Meixner: e.g. we are not parts, but probably constituents of states of affairs.
Einführung in die Ontologie Darmstadt 2004