A HIERARCHY OF UNIVERSALS
We have argued for scientific realism, metaphysical realism, and modal realism. The last two should, in fact, be thought of as part of the overall commitment of scientific realism, since science does include mathematics and logic. Mathematics furnishes a powerful argument for metaphysical realism. And logic, construed to include probability, involves necessity and related issues concerning possibilia and thereby furnishes a powerful argument for modal realism. We characterize this position as scientific Platonism. In addition, we have argued for semantic realism. Anyone who accepts any of the other realisms should also believe in reference and truth.
It is important to remember that, in our usage, a realist can be neutral on questions of reductionism. In defending realism about physical objects, universals, possibilia, truth, and reference, we leave ourselves the task of investigating what these things are, what they are constructed of, whether they are reducible to entities of some specifiable sort, and so forth.
We begin by considering universals: what are they? One crucial feature of (many) universals is their ability to be in several places at once. They, or at least some of them, are recurrence We should not, however, place too much weight on plural localization as a defining characteristic of universals. Not all universals are multiply located. Some are hard to locate, with any plausibility, anywhere at all. Admittedly, a property is plausibly locatable when it is instantiated by something spatial: it is located wherever its instances are.