The idea that theoretical or even metaphysical notions influence the meaning and perception of scientific evidence has by now garnered widespread acceptance. The road to this conviction has taken many steps. French scientist Pierre Duhem is considered one of the first thinkers to note the theoretical commitments of empirical scientific investigation—the later so-called theory-ladenness. For him, the result of a physics experiment is the fruit of an observation interpreted by virtue of the theories held by the observer. When using their instruments, physicists, chemists, and physiologists “implicitly admit the accuracy of the theories justifying the use of these pieces of apparatus as well as of the theories giving meaning to the abstract ideas of temperature, pressure, …” ([1], pp. 259–60).

In The Logic of Scientific Discovery (1934), Karl Popper wrote that “for even singular statements are always interpretations of the ‘facts’ in the light of theories” ([2], p. 423, italics in the original). Popper notes that any descriptive statement contains universals, which are hypotheses or conjectures; given that, for him, “universals cannot be correlated with any specific sense—experience” ([2], p. 95)—because “they transcend experience” ([2], p. 424)—these propositions cannot be verified. A scientific community convention is then required to establish an empirical basis ([2], Chap. 5).

In 1951, Quine challenged the analytic–synthetic distinction, arguing that empirical propositions cannot be isolated from their associated theories. As a result, there is “a blurring of the supposed boundary between speculative metaphysics and natural science” ([3], p. 20). Hans-Georg Gadamer, affiliated with a different tradition (hermeneutics), refers to the “horizon”, “the range of vision that includes everything that can be seen from a particular vantage point” ([4], p. 302).

In 1958, Hanson coined the expression theory-ladenness in his well-known statement: “seeing is a ‘theory-laden’ undertaking” ([5], p. 19). Much has been said about the meaning and scope of his notion and the concept of incommensurability set forth by Thomas S. Kuhn and Paul K. Feyerabend. Because both thinkers underwent an intellectual evolution over the years, a moderate interpretation of their theses may be considered. While relevant differences separate the ideas of all the authors mentioned above, e.g., (Heildelberger [6]), a certain influence of theory in observations and experiments remains undisputed and clear. This influence may be conceptual or semantic—the meaning of observational terms is (partially) determined by theory—or “perceptual”, by the cognitive theory biases of the observers.

Empiricist Bas van Fraasen ([7], p. 81) also supports theory-ladenness. More recently, Jim Bogen explained that “by Bayes’ theorem, the conditional probability of the claim of interest will depend in part on that claim’s prior probability. (…) One’s use of evidence to evaluate a theory depends in part on one’s theoretical commitments” ([8], p. 11). Additionally, Julian Reiss complained that evidence theories fail to take into account that evidence about “a hypothesis is dependent on how the world works and our knowledge there of” ([9], p. 302). In summary, as James Ladyman pointed out, “the degree of confirmation of a scientific theory is heavily theory-dependent, in the sense that background theories inform judgments about the extent to which different theories are supported by the available evidence” ([10], p. 214).

Finally, moving beyond this thread of thought, Craig Dilworth [11] underscored that modern science applies specific, fundamental metaphysical principles (uniformity of nature, substance and causality), which outline a physicalist, deterministic (though not rigid) view of reality that is not accepted without reservations by all scientific disciplines, depending on their subject. These principles determine what is ontologically necessary or possible within every discipline, provide the structure of scientific rationality, set guidelines for developing science, and define the basic concepts. They are not necessarily true, but it is assumed that they were.

Aggazi ([12], p. 19; quoted by 1, p. 71) states:

Science […] cannot be pursued without one’s using certain criteria of intelligibility which are prior to the specific tasks it involves. In fact, every advancement of some science which has been presented as a ‘liberation from metaphysics’ has actually been tantamount to discarding a particular metaphysical framework and accepting (often unconsciously) a different one […] Therefore it is much more reasonable to be aware of the metaphysics one has, rather than have a metaphysics without knowing it.

Dilworth shows how these metaphysical criteria or principles have shaped the methodology of the empirical aspects of science. Regarding him, we should mention ‘principle-laden’ (cf. [11], p. 94) concepts, rather than theory-laden notions. “Neither these principles,” Dilworth argued, “nor the physicalistic interpretation they have been given by modern science are inviolable, however, and to a large extent both have been adopted” ([11], p. 193). In his paper on “the metaphysics of neuroeconomics”, Michiru Nagatsu admited that “metaphysics is an indispensable part of scientific practice that provides scientists with worldviews and directions in research” ([13], p. 198).

In short, metaphysics—understood as a worldview—is always present in science, and the current metaphysics of science is materialistic. As Schouten and Looren de Jong simply put it, “science and philosophy have turned materialist: all that exists exists in space and time and must be considered fundamentally physical” ([14], p. 1). Let us see how this applies to neurosciences, economics, and neuroeconomics.

Dilworth ([11], p. 265) notes:

The fundamental problem for modern science with regard to the spirit is evident already in early Greek atomism, with its lacking categories for the self and psychic states. This problem remains in modern science, both as a paradox with respect to the nature of its own activities, as well as a major lacuna with respect to what it is capable of explaining. […] [T]he spiritual element generally acknowledged to exist in human activities cries for explanation. Science, limited as it is to physicalistic categories, cannot handle either of these issues.

Indeed, this limitation introduces a tension in the philosophy of neurosciences. Though a complete materialistic reductionism largely prevails (e.g., Patricia and Paul Churchland), not all authors share this belief. Morality, responsibility, complex or high reasoning, conscience, affective relations are evident realities pointing to something beyond matter. Finally, many reductionists cannot accept that all can be explained by biological interactions. David Chalmers [15] spoke about an explanatory gap, or “the hard problem of consciousness”, while Bickle et al. ([16], p. 11) wondered, “Why should that particular brain experience give rise to conscious experience?” The introspective aspect of individual sensory experiences also raises doubts.

Bennett and Hacker ([17], Part I, Chap. 3) argued that neuroscientists are plagued by a “mereological fallacy”, attributing psychological acts pertaining to the whole human being to a part of him—the brain or the mind. That idea is drawn from Aristotle, who wrote in De Anima: “To say that the soul gets angry is as if one were to say that the soul weaves or builds a house. Probably it is better not to say that the soul pities, or learns, or thinks, but to say that the soul is the instrument whereby man does these things” (On the Soul 408b 12–15, [18]). Anthony Kenny [19] referred to that mistake as “the homunculus fallacy”, while Wittgenstein noted that “only of a living human being can one say it has sensations; it sees, is blind; hears, is deaf; is conscious or unconscious” (Philosophical Investigations, & 281, [20], p. 97c). The human being is an organic whole not reducible to the sum of its parts. Voices have also risen against materialist reductionism in psychiatry and psychology. More generally, William Wimsatt (e.g., [21]) spoke about “functional localization fallacies”—that is, attributing a property of the whole to one of its parts.

However, this is not the dominant view, which is mainly reductionist. The topic of reductionism is thoroughly complex and, although tensions in this field still remain, the balance is inclined toward an epistemological and ontological reduction of the mind to the neural, according to the underlying physicalist worldview. Yet the situation is not hopeless: in the introduction to their book on reductionism, after saying that the most reductionist position on the book is John Bickle’s, Schouten and Looren de Jong ([14], p. 21) concluded:

Most other authors, however, will acknowledge that to a more or lesser degree higher-level explanations are indispensable, but not autonomous; and that psychology and neuroscience are and should be connected and perhaps integrated, but not unified along physicalist lines.

While avoiding a dualistic view of the human being, Aristotle’s hylemorphic conception of the soul as the form of the body allows for two compatible non-reductionist explanations (On the Soul 403a 39–403b 2) [18]:

The natural philosopher [the scientist] and the logician [philosopher, psychologist] will in every case offer different definitions, e.g., in answer to the question what is anger. The latter will call it a craving for retaliation, or something of the sort; the former will describe it as a surging of the blood and heat around the heart. The one is describing the matter, the other the form or formula of the essence.

Nonetheless, to make these explanations compatible, physicalism must be replaced by another metaphysical naturalist—yet not a materialist view.

There is a parallel problem in the application of modern science’s physicalist, metaphysical commitment to social science. Dilworth ([11], p. 130) explains,

Some of the basic problems regarding their applicability in the social sciences are those of synthesizing uniformity and free will, the vagueness apparently inherent in the notion of a social substance, and the dominant position occupied in social thought by the notion of final causes.

These characteristics also introduce a tension to social sciences, including economics, as Dilworth once again points out, specifically about economics and freedom ([11], p. 135):

[T]here is a particular tension in the economist’s conception of human nature. On the one hand the notion of free will is integral to it, since without free will the rationality principle would make no sense. On the other hand, however, no economic actor has the freedom not to follow the rationality principle, which itself determines how he or she is to act.

Throughout the nineteenth and early twentieth centuries, economics was closely related to psychology. Freedom was present, but not always the star. The roots of the law of decreasing marginal utility lie in psychology, and the view of utility from authors such as Gossen, Jevons, Menger, Walras, and Marshall are also associated with psychology. For Keynes, psychological factors strongly influence behavior. However, it should be noted that the ordinal utility theory, which started with Pareto, Hicks and Allen, and Slutsky, began to belittle psychology, planting the seeds of a “logical”, non-psychological, theory of rational choice, the core of a formal science of economics.

Let us take a glance through history. Economics started to become a formal science in the nineteenth century. Nassau Senior was the first economist to strongly argue against consideration of ends and the normative character of economics, maintaining the distinction between positive or neutral analysis and providing recommendations for economic policy in his Outline of Political Economy (1836). In 1860 he delivered the presidential address to Section F (“Economic Science and Statistics”) of the British Association for the Advancement of Science ([22], pp. 19–24). As Terence Hutchinson ([23], p. 9) remarked, “Section F had to assert its scientific respectability and its worthiness to be included alongside the established subjects of natural science”. According to Hutchison ([23], p. 13), Senior sketched a narrow and limited vision of economic science. In other words, under the pressure of natural sciences requirements, economic science was forced to modify its subject of study in order to conform to this particular conception of science.

Thus, we arrive at the definition formulated by Robbins ([24], p. 15) –influenced by Menger, Weber and Mises: “Economics is the science which studies human behavior as a relationship between ends and scarce means which have various applications.” That is to say, economics is the science of a specific vision of choice. In this way, economic science is turned into a formal science. It is formal because its subject of study is not a field related to material human needs, nor to production and distribution. It becomes a choice, any choice, to the extent that it requires adaptation of means to certain ends: it is an approach to human action. In fact, it was initially correlated with economic matter, viewed as efficient distribution of resources, but it quickly applied its logic to the analysis of other human realities.

The key to fitting human action in a specific framework is to consider ends or preferences as given. Stable, exogenous preferences (the ends, as considered by economics) prepare the field for the development of a certain scientific subject. Menger entitled Appendix VI of his Investigations into the Method of the Social Sciences with Special Reference to Economics “The Starting Point and Goal of all Human Activity are Strictly Determined”. In that work ([25], p. 217) he sustained that “[e]conomy is really nothing else than the way which we travel from the previously indicated starting point of human activity to the previously indicated goal.” Strictly speaking, it is a technical path that enables formulation of exact laws whose formal nature does not differ from that of the laws of all other exact sciences and of the exact natural sciences, particularly (cf. [25], pp. 217–219). Therefore, economic science considers ends as given. As Robbins ([24], p. 29) maintains, “economics is not concerned at all with any ends, as such. It is concerned with ends in so far as they affect the disposition of means. It takes the ends as given in scales of relative valuation”. Freedom is thus put into brackets.