According to Feser, modern conservatism can be divided into three broad metaphysical categories: Realist Conservatism, Reductionist Conservatism, and Anti-Realist Conservatism.
Realist Conservatism, Feser says, “affirms the existence of an objective order of forms or universals that define the natures of things, including human nature, and what it seeks to conserve are just those institutions reflecting a recognition and respect for this objective order. Since human nature is, on this view, objective and universal, long-standing moral and cultural traditions are bound to reflect it and thus have a presumption in their favor.”
Reductionist Conservatism, he says, “might be defined as a variety of conservatism that agrees with Realist Conservatism in affirming that there is such a thing as human nature and that it is more or less fixed, but which would ground this affirmation, not in anything like an eternal realm of Forms, but rather in, say, certain contingent facts about human biology, or perhaps in the laws of economics or in a theory of cultural evolution. The Reductionist Conservative is, accordingly, more likely to look to empirical science for inspiration than to philosophy or theology. He is also bound to see grey in at least some areas where the Realist Conservative sees black and white, since facts about economics, human biology, and the like, while very stable, are not quite as fixed or implacable as the Forms. But he is less likely to see grey than is the Anti-Realist Conservative…”
An Anti-Realist Conservative, he says, “might be characterized as someone doubtful that any relatively fixed moral or political principles can be read off even from scientific or economic facts about the human condition. Whereas Realist and Reductionist Conservatives value tradition because there is at least a presumption that it reflects human nature, the Anti-Realist Conservative values it merely because it provides for stability and order.”
Feser notes that Realist Conservatism must be supported because it is a true form of conservatism. He rejects Reductionist Conservatism and Anti-Realist Conservatism—noting that these two are not really versions of conservatism at all, any more than nominalism or conceptualism are versions of realism. He writes: “For the Anti-Realist Conservative, as I've said, does not really oppose liberal measures per se, but only their overhasty and excessively disruptive implementation. Historically, the pragmatists, politicians, and others who exemplify Anti-Realist Conservatism have merely served to consolidate the gains of liberalism.”