  If we add the functor ε (read as “is”) forming sentences from two names, we obtain Leśniewski’s ontology (LO). The meaning of the constant ε is perhaps the most important matter for a proper understanding of LO. The epsilon corresponds well to the sense of the copula “est” in Latin sentences of the type “Socrates est homo”. The epsilon has no spatio-temporal connotations and does not indicate the membership relation or identity. The rendering of the epsilon by the English “is” may be misleading, because the latter is modified by articles. The axiomatic characterization of the meaning of the epsilon is given by