Psychophysics represents one of the most ambitious and controversial ventures of modern thought. Emerging from the problematic legacy of Cartesian dualism between res cogitans and res extensa, the idea of an exact science of the soul has been the subject of various and authoritative attempts at a foundation, oriented towards formulating laws capable of explaining the dynamics of psychic events based on a presumed analogy with external events. These efforts found an initial rigorous manifestation in the psychometric hypotheses presented by Christian Wolff in his Psychologia empirica (1732) and Philosophia practica universalis (1738-39), and spanned the whole Enlightenment and nineteenth-century German philosophy, rapidly intertwining with advancements in the fields of physics, optics, and sensory physiology. However, the Enlightenment flourishing of “physical psychology” encountered an important obstacle with Kant’s denial of the possibility of a mathematical treatment of the soul, as contained in his Metaphysische Anfangsgründe der Naturwissenschaft (1786). Kant’s opposition to psychometry was far from unequivocal: on one hand, he assigned empirical psychology to the realm of anthropology, thus not entirely stripping it of epistemic legitimacy; on the other hand, he paved the way for subsequent developments in psychophysics by formulating, already in his Critique of Pure Reason (1781), the highly relevant notion of “intensive magnitude”.
Kant’s interdiction only momentarily delayed the emergence of theories associated with the psychophysical idea, which would emerge systematically during the nineteenth-century German philosophical period. Romantic science – with authors such as Johann Wilhelm Ritter (1776-1810), Carl Friedrich Kielmeyer (1765-1844), Lorenz Oken (1779-1851), and Karl Friedrich Burdach (1776-1847) – would undertake the task of reactivating the link between philosophy and physiology, attempting to reconcile the demands introduced by Kantianism with new directions in the study of the living. Shortly thereafter, Herbart’s seminal 1822 lecture to the Königslichen Deutschen Gesellschaft, Über die Möglichkeit und Nothwendigkeit, Mathematik auf Psychologie anzuwenden, would lay the basis for a mathematical foundation of psychology, thus giving a decisive impulse to the emergence of a true Herbartian psychological tradition represented by Wilhelm Fridolin Volkmann (1801-1877) and Theodor Waitz (1821-1864), alongside figures such as Ludwig Strümpell (1812-1899) and Moritz Wilhelm Drobisch (1802-1896). Herbart’s attempt to mathematically quantify conscious events, his critique of Kantian Vermögenspsychologie, and his formulation of the concept of a “threshold of consciousness” enjoyed considerable success in the philosophical and psychological debates of late nineteenth-century Germany, becoming an indispensable reference for generations of physiologists seeking to establish points of contact between the psychic principle and the perceptual apparatus. In this regard, two traditions can be identified: the first, originating from the laboratory of Johannes von Müller (1752-1809), with prominent representatives such as Hermann von Helmholtz (1821-1894), Emil Du Bois-Reymond (1818-1896), and Rudolf Virchow (1821-1902); the second centered around the University of Leipzig, with figures such as Ernst Heinrich Weber (1795-1878), Carl Ludwig (1816-1895), Gustav Fechner (1801-1887), and Wilhelm Wundt (1832-1920).
For Helmholtz, it was the physiology of the senses that, as early as in 1855, provided the exact point where philosophy and natural sciences “draw closer”, defining the contours of that “boundary region” where the two branches of knowledge recognized under the names of Natur- and Geisteswissenschaften more generally diverge. With Fechner and Wundt, the trajectory of German psychophysics reached its peak. While Fechner, in his Elemente der Psychophysik (1860), designated psychophysics as the exact doctrine of the relationships between the soul and the body, having substantiated Weber’s mathematical studies on the connection between stimulus and perception with experimental evidence, Wundt addressed – almost concurrently – the issues concerning the measurement of the “magnitude” of sensations, characterizing this effort in his Vorlesungen über Menschen- und Thierseele (1863) as the “first step in the bold enterprise of applying an exact measure to the magnitudes of what is spirit”. From then on, according to Wundt, psychology was to remain indebted to Fechner for his “first exhaustive examination of sensory sensations from a physical perspective, which laid the foundation for an exact theory of sensation”. This marked the scientific foundation of an experimental-based psychology.
Fechner and Wundt represent the apex of nineteenth-century German philosophical and psychological reflection on the possibility of reconciling the continuous and indivisible interiority of the psyche with the quantitative measurement of partes extra partes. The legacy of their scientific insights was carried forward already in the second half of the nineteenth century in other European philosophical contexts: in France by Alfred Binet (1857-1911) and Théodore Simon (1873-1961), in Italy by Francesco De Sarlo (1864-1937) and later by Antonio Aliotta (1881-1964), and in the Anglo-Saxon world by Edward Titchener (1867-1927) and the behaviorist theories. Behaviorism, in particular, marked a fundamental departure from Wundtian structuralism by abandoning the problematic framework of Cartesian dualism and introducing the concept of the “observable manifestations” of the soul. In this context, renewed attempts at the mathematization and formalization of psychology have been made, such as in the studies of Clark Leonard Hull, Mathematico-Deductive Theory of Rote Learning (1940) and Principles of Behavior (1943). However, this is only one among many twentieth-century developments of psychophysics. The more recent history of this field is far from concluded and remains to be written.
For the upcoming special issue of Discipline Filosofiche, contributions on this topic are invited, encouraging the treatment of the following subjects:
1) the modern philosophical presuppositions of the psychophysical idea;
2) Wolffian psychometry and the eighteenth-century debate;
3) empirical psychology in Kant and Kantianism;
4) the psychological debate in nineteenth-century Germany from Herbart to Wundt;
5) the philosophy and psychology of Gustav Theodor Fechner;
6) psychophysics in France, the United States, England, and Italy;
7) the fortune and developments of psychophysics in the twentieth century;
8) philosophy of experimental psychology.

Guidelines for the authors: Submissions should not exceed 9,000 words including abstract, refer-ences and footnotes. Manuscripts may be submitted in Italian, English, French, German, or Spanish. They must be sent as an email attachment in .doc or .docx format, along with a .pdf version, to Chiara Russo Krauss (chiara.russokrauss@unina.it) and to Giuseppe Guastamacchia (giuseppe.guastamacchia@unito.it). Submitted manuscripts will be sent to two independent reviewers, following a double-blind peer review process. The reviewers may ask authors to make changes or improvements to their contributions in view of publication. Authors are kindly requested to attach both an anonymous version of their contribution entitled “Manuscript” and a separate “Cover Page” stating their name, academic affiliation and contact details. Manuscripts must include an English abstract of less than 150 words and 5 keywords. Any property of the file that might identify the author must be removed to ensure anonymity during the review process. A notification of receipt will be issued for each submission. In drafting their text, authors can adopt any clear and coherent style, but should the text be accepted for publication, they will be required to send a final version in keeping with the style guidelines of the journal (please refer to the style guidelines at https://www.disciplinefilosofiche.it/en/norme-redazionali/). Submission of a manuscript is understood to imply that the paper has not been published before and that it is not being considered for publication by any other journal. Should the manuscript be accepted for publication, the author will be required to transfer copyrights to the University of Bologna. Requests to republish the article may be made to the Editorial Board of the Journal.

Deadline for the submission of manuscripts: January 16, 2026
Notification of acceptance, conditional acceptance, or rejection: February 27, 2026
Deadline for the submission of the final draft: April 14, 2026

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