Hazen, A.P., Against Pluralism, Australasian Journal of Philosophy, 71:2 (1993:June) p.132

By pluralism I mean the doctrine that the higher-order quantifications of what are formally systems of second-order logic may be interpreted as employing an irreducibly plural kind of quantification over the entities that form the domain of the first-order quantifiers of the system, and that the use of the resources of (monadic) second-order logic therefore carries no ontological commitment to any entities - sets, classes, Fregean 'concepts' what have you - beyond the ones over which we take the first-order variables to range.