With his Australian colleague David Macarthur, De Caro espouses a broadening of today's "scientific naturalism" - which tends to be an eliminative materialism - to address in a non-reductionist way features like norms, beliefs, and values. They hope to combine the "scientific image" and "manifest image" of Wilfrid Sellars.

What makes Scientific Naturalism and Liberal Naturalism both versions of naturalism is that neither countenances the supernatural, whether in the form of entities (such as God, spirits, entelechies, or Cartesian minds), events (such as miracles or magic), or epistemic faculties (such as mystical insight or spiritual intuition). The importance of this for the philosophical approach to normativity is that any form of naturalism will be opposed to Platonism about norms, where this is understood as the view that normative facts hold wholly independently of human practices (say, of reason giving) and are, as it were, simply there anyway waiting to be discovered. For similar reasons it will be opposed to a Moorean non-naturalism that holds that our access to normative facts is by way of a sui generis epistemic faculty of intuition directed at just this kind of fact. And of course it will be opposed to any theistic foundation for normative facts or our access to them.

(Naturalism and Normativity, Harvard University Press, 2004, p.3)

De Caro has written several articles and a book surveying a "galaxy" of problems surrounding the questions of human action, free will, and moral responsibility. In his 2004 book, Il libero arbitrio, De Caro lists the four historic problems with indeterminism:

• The inability to explain agent control (the crux of libertarianism, he says)
• The risk of an obscure metaphysics
• The danger of infinite regress
• The problem of localizing the time and place of indeterminism

In his discussions of determinism, De Caro describes how compatibilists accept the idea that they have freedom of action as long as they are not being coerced, even if they lack the freedom to choose or "free will." He reviews the Consequence Argument of Peter van Inwagen. And he discusses an attempt by Donald Davidson to reconcile determinism with free will in a physically monistic world by interpreting mental properties as "anomalous."

As is well=known, Davidson argues that mental events are irreducible to physical events. Davidson's "anomaly" is an explicit defense of human freedom and autonomy, says De Caro, which he traces back to an idea of Kant. Davidson's argument for an "anomalous monism "is one of the most complex arguments debated in contemporary analytic philosophy, he says, but it is shown to fail by Jaegwon Kim's arguments against the emergence of a non-reductive physicalism.

Moreover, De Caro says, where Kant was a libertarian, Davidson is a compatibilist, because he defines freedom as the ability to act without hindrance or coercion. In his last years, Willard van Orman Quine accepted Davidson's anomalous monism, says De Caro. Quine was a compatibilist who hoped for as much determinism as quantum physics would allow him, as a principle of reason itself. Most compatibilists agreed with Quine, says De Caro, holding a position called supercompatibilism, in which determinism is not merely compatible with free will, it is a necessary requirement. De Caro cites Moritz Schlick, A. J. Ayer, and quotes R.E. Hobart, who said that determination (not determinism) is required for free will.

De Caro describes the standard argument against free will.

[I]ndeterminism by itself—far from automatically generating freedom—produces only randomness.

However, a different question can also be asked with regard to this issue: does indeterminism also make freedom impossible, as it is frequently maintained? Or, to put it differently, can it not be that the addition of some other factors to indeterminism may make freedom possible, as libertarians (who think that freedom requires indeterminism) argue?

At this stage, however, one should notice that the above-stated argument against unreflective libertarianism clearly shows that philosophy, with its conceptual clarifications and analyses, has an essential role to play in the discussion on free will. It accomplishes this by determining the correct scope and the conditions of use of the concepts involved, and by evaluating the relevance of empirical evidence. In this sense, philosophy’s role is not confined to assessing the relation between indeterminism and freedom. Another example is the very common view that, if our actions were determined, ipso facto we would lack freedom.

("How To Deal With The Free Will Issue," in Cartographies of the Mind, Springer, 2007, pp.260-61)

Consistent with his theory of a "liberal naturalism," De Caro promotes the idea of "pluralism," in which conceptual analysis and empirical science play complementary roles.

What all this shows is only that science cannot play an exclusive role in the free will discussion. It does not show that it cannot, and perhaps should not, complement conceptual analysis. Actually, most of the major views imply that, if free will has to be real, the natural world has to be structured in an adequate way (a way that each view describes in its own terms). Certainly, determining the structure of the world is a task for empirical science. In this sense, according to many, the empirical evidence mentioned in the previous paragraph is very relevant. This is a methodological stance I call "pluralism," the view according to which, besides conceptual analysis, the investigation on free will also requires that empirical research explain how the natural world actually works.

("How To Deal With The Free Will Issue," p.262)