We live with a fractured sense of self. In our modern, popular understanding, the mind is often presented as inherently divided, a house divided between two opposing faculties. On one side stands reason: slow, logical, cool-headed, and judicious. On the other stands emotion: fast, impulsive, hot, and irrational. This binary is so deeply embedded in our language and psychology that we treat it as a fundamental truth of the human condition.
This common-sense split is not merely a folk theory; it has long been the "standard approach" in formal philosophy and cognitive science. These disciplines have historically treated reason and emotion as "fully independent cognitive faculties" [1]. This framework allowed for a clean separation, suggesting their respective causal contributions to any given thought or judgment could be neatly isolated.
But, this comfortable division is dissolving. In recent decades, a "revolution in the science of emotion" has begun, one that is creating a "paradigm shift" in how we understand decision-making [2]. This new wave of research reveals that emotions are not irrational static; rather, they are "potent, pervasive, predictable... drivers of decision making". Neuroscience, too, has moved past a simple cause-and-effect model. It is increasingly moving toward an integrated view where a feeling and its biological expression are not a sequence, but two phases of the same unbroken activity [3].
This contemporary scientific "paradigm shift", however, is not so much a discovery as it is a restoration. The very "problem" that modern science is "solving"—the idea of a disembodied reason at war with a chaotic emotion—is not a timeless psychological fact. It is a piece of cultural wreckage, a historical artifact. The "traditional rational choice theory" that new research is now "synthesizing" with emotion is not the original philosophy of the 18th century. It is the caricature of it. If this split is not a scientific absolute, we must ask: where did it come from? This chapter argues that its origins lie not in a timeless truth, but in a highly effective act of historical branding, a moment when one intellectual movement manufactured its own opponent.
The story of our fractured self begins with the movement that prided itself on championing emotion: Romanticism. Originating in Europe near the end of the 18th century, the Romantic movement defined itself, first and foremost, in opposition. Its intellectual purpose was conceived "in response to the Age of Enlightenment". It was, as many sources describe it, a reaction against the 18th-century rationalism.
To have a reaction, one must have a clear target. The Romantics, in their art and philosophy, constructed a powerful one. They defined the preceding era as an "ordered world of Enlightenment thought" [4], one obsessed with "rationalism and classicism," order, calm, harmony, and balance.
Against this "ordered world," Romanticism championed its direct opposites: the individual, the subjective, the irrational, the imaginative, and the spontaneous. It placed a premium on emotions/feelings and individual experience above logical thought. This created a simplistic but potent binary. In a famous encapsulation of this critique, the "man of the enlightenment" looks at a rainbow and, like Newton, "break[s] the rainbow down into its constituent parts," destroying its magic. The "romantic," by contrast, is "transfixed by its beauty".
This "romantic critique of enlightenment rationality" was a specific and powerful argument. It claimed that the 18th century's "overreliance on rationality" and its "mechanistic views of humanity" had dangerously neglected "the emotional, spiritual, and imaginative aspects of human experience". To give this intellectual antagonist a name, a label was elevated and popularized: "The Age of Reason". This description was later immensely popularized through the construction of modern education systems, which codified this simplified historical narrative into textbooks and curricula, cementing it in the popular imagination across generations.
This label, which we now often take as a neutral historical descriptor, was, in effect, a pejorative reduction. It was a "convenient fiction," a modern distortion [5]. This act of branding was not only polemical; it was essential for the Romantic movement's self-conception. The Romantics did not, in fact, discover emotion. They re-branded it. As will be shown, they took the "sensibility" and "sentiment" that were already central to 18th-century culture, radicalized them into a more individualistic form, and then erased their origins by painting the previous era as cold, "rational," and "mechanistic."
This caricature was so successful that it has been accepted by both modern defenders and detractors of the Enlightenment [6]. Both those who call for a "reboot of the Enlightenment" to defend science, and those who see it as a "pathology" that leads to domination, make the same "collective error": they both accept "that the Enlightenment was a movement of reason opposed to the passions". They are, in effect, arguing over a phantom. The Enlightenment was not solely about science—it was about human wellbeing in many forms and an opposition to superstition.
The first step in dismantling this phantom is to look at the label itself. The "Age of Reason" is a profoundly misleading name for the 18th century. As the Stanford Encyclopedia of Philosophy notes, while there was an "enthusiasm for reason," this enthusiasm was not primarily for "the faculty of reason as an independent source of knowledge." That concept, a holdover from 17th-century rationalism, was, in fact, "embattled" during the 18th century [7].
The intellectual movement in the ascendant was not pure rationalism, but empiricism. We must distinguish between the "rationalist strain" founded by René Descartes—which prioritized a priori reason and innate ideas, and was often skeptical of the senses—and the "empiricist strain" founded by Francis Bacon and championed by John Locke and David Hume.
This empiricist strain, which became the dominant force in the Enlightenment, argued the precise opposite of the "cold reason" caricature. It argued that all knowledge "originates from sensory experience". John Locke, a foundational Enlightenment thinker, wrote his An Essay Concerning Human Understanding as a direct assault on the rationalist doctrine of innate ideas. For Locke, the mind is a tabula rasa, a "blank piece of paper" [8]. All of its ideas, without exception, come from "experience," which he defined as either "sensation" (perceiving the external world) or "reflection" (perceiving the operations of our own minds).
This is not a philosophy of "cold reason" divorced from life. It is an "experience-first" philosophy that, by its very nature, demands engagement with "the physical world". Locke's empiricism is considered "paradigmatic of the ideals of the Enlightenment" precisely because it insists on "evidence" and "empirical observation". This "bottom-up" approach, exemplified by Bacon and Newton, was the era's defining feature, not the "top-down" metaphysics of the rationalists.
The central Romantic critique—that the Enlightenment "disregarded human emotions, imagination, and the complexities of individual experience"—is thus aimed at the wrong target. The actual Enlightenment was founded on experience. The Romantics were not introducing experience to a movement that had ignored it; they were re-interpreting it. They disliked the conclusions the empiricists drew from experience (such as a "mechanistic" understanding of the universe), and so they championed a different kind of experience—subjective, emotional, and sublime—over the sensory, observable, data-driven experience of the empiricists. To claim the Enlightenment ignored experience is the foundational distortion of the strawman.
This brings us to the most direct refutation of the "cold reason" caricature, and it comes from one of the Enlightenment's most formidable figures, David Hume. A central pillar of the Scottish Enlightenment, Hume's work on human psychology stands as a stark rejection of the idea that reason did, or even could, rule the mind.