The distinctive scholarly stake of Kant’s Early Critics: The Empiricist Critique of the Theoretical Philosophy lies in its reconstruction—through first-time English translations and a programmatic editorial introduction—of the earliest, empiricist-leaning attempts to read, resist, and retool the Critique of Pure Reason between 1781 and 1789. Sassen’s contribution is not merely curatorial. By arranging reviews, essays, and rejoinders around the Aesthetic, the idealism question, and the Analytic of concepts, she displays how a set of problems—origin of spatial representation, the criterion of objectivity, the charge of “higher idealism,” the status of categories—coheres into a running pressure on Kant’s method and, in turn, conditions the B-edition revisions. The volume thereby makes visible a reception history that both codifies and destabilizes Kant’s first system, while furnishing the textual levers with which the second is pried open.
Sassen frames the dossier by recovering an initial quiet that Kant had not anticipated and a first review that he certainly had not desired. The correspondence and public record show him hoping for close study by Mendelssohn and Tetens, only to meet silence in 1781 and a brusquely schematic verdict in 1782—the Göttingen (Feder/Garve) review—that he answered, with visible agitation, in the Appendix to the Prolegomena. What one now encounters, thanks to Sassen’s editorial scaffolding, is a scene where the empiricist tendency—Locke, Hume, Scottish common sense—supplies the idiom in which early readers try to domesticate the Critique. This empiricist wave shapes the debate from 1782 until roughly 1788; only then do the “rationalists” (Eberhard, Maaß, Schwab) enter, with Reinhold and, soon, Fichte pointing reception towards the constructive idealisms of the 1790s. Sassen’s delimitation to 1782–1789 is both archival and argumentative: it captures the stretch in which empiricist pressure most directly impinges on Kant’s theoretical project and in which many of the impulses ferment. The introduction sorts three currents—empiricist, rationalist, and forward-developing scholars—and explains why the first matters most for the way the Critique rewrites itself.
Everything turns on reception as problem formation rather than on reception as mere opinion. Sassen’s editorial narrative insists that the Feder/Garve complex did not simply misdescribe Kant; it condensed a set of worries that the Kantian text had not yet learned to answer in public prose. At issue is the image of a subject whose understanding makes objects by synthesizing “a multiplicity of small successive alterations of our soul” into a world laid out in time and space, with lawlike form supplied a priori. The reviewers press the unsettling corollary: if sensation contributes no directive constraint, how does one non-arbitrarily fix a synthesis and, with it, a distinction between reality and illusion? Kant’s Prolegomena reply, fixated on banishing a Berkeleyan comparison, leaves this objection structurally intact; it is precisely the sense in which empirical matter appears nondirective that will haunt early empiricists and force subsequent Kantian revisions. Sassen’s exposition does not adjudicate; it exhibits the argumentative gears by which the objection gains traction.
Hence the constructive tension on which the volume turns: empiricism asks how the given—felt, seen, moved-through—guides combination; Kant insists the very norms of objective unity must be in place for any given to count as such. The early reviewers exploit the interval between these claims. Reading Garve’s longer, more temperate review alongside the Göttingen piece isolates the crux. Garve refrains from the epithet “idealism,” yet he keeps a wary eye on two fronts: the Fourth Paralogism’s sufficiency to secure external existence and the apparent inability, within Kant’s picture, to demarcate dreams from veridical experience. Sassen shows how Kant’s private generosity to Garve (he praises fairness and philosophical seriousness) contrasts with the public polemics flung at the anonymous Göttingen critic; but she also shows that the contentual discomforts are almost the same in both reviews. The difference is one of rhetorical temperature, not of conceptual pressure.
When the dossier turns to the Transcendental Aesthetic, Sassen arranges Tiedemann, Feder, and Pistorius so that Kant’s claim to the a priori form of space and time is approached from three angles: a challenge to the synthetic character of mathematics; an empiricist genealogy of spatial concepts (sight, touch, kinesthesia); and a hybrid, “neglected alternative” that assigns space/time a dual status, subjective form and objective feature. Tiedemann’s provocation—treating 7+5=12 as analytic in a mereological sense and the straight-line principle as an evident relation disclosed by conceptual comparison—aims at the Kantian hinge between intuition and concept. Sassen underlines that Kant would counter by invoking the necessity of spatial intuition to any such comparison: one does not juxtapose pure concepts but images governed by the form of space. What matters, for her editorial construction, is not the victory but the forcing move: the empiricist can reclassify the terrain so that the Kantian distinction analytic/synthetic must work harder than its own luminous simplicity suggests.
Feder’s On Space and Causality elaborates the empiricist path by mobilizing visual and tactual phenomenology and work on the Molyneux question to argue for an experiential derivation of spatial representation, and by scrutinizing the Aesthetic’s metaphysical exposition point by point. One consequence is the recurrent “psychological” reading of a priori as temporally prior in the mind: a native template antecedent to experience. Sassen observes that even Kant’s defenders, writing in the Allgemeine Literatur-Zeitung, tacitly share this temporality-psychology frame, thus answering Feder with empirical considerations of their own. The upshot is revealing. Before an epistemic-transcendental interpretation stabilizes, nineteenth-century debates on perception will inherit—and retool—this psychological register of the Aesthetic. Sassen neither endorses nor rebukes; she documents a contextual grammar that shaped how “a priori form” could be heard at all.
Pistorius stands at the center of Sassen’s composition because he articulates three knots of resistance with exceptional clarity: affection (how can a thing in itself affect us if causality is restricted to experience?), the neglected alternative (why could space/time not be both subjective form and property of things), and subjectivity (does the Kantian restriction strand us within our own representations?). Reviewing Schultz’s Kantian Elucidations, Pistorius charges that the very insistence on the subjectivity of form, taken together with affection talk, jeopardizes the connection between the intelligible and the sensible: the “objective intelligible world” risks erasure. His constructive counterproposal is carefully two-tiered: general features of space/time track our constitution (our limitation), whereas specific determinations are anchored in the objects that affect us. Sassen captures both the ingenuity and the precariousness of this move: if the general features are “from us,” why would things in themselves accord with them? And if they just happen to accord, why is this harmony anything but luck? Here the empiricist critic half-absorbs the Copernican turn only to turn it back, alleging that the Kantian strategy legislates conformity without sufficient right. The effect of Sassen’s ordering is to make Pistorius’s hybrid proposal the hinge on which the section swings from critique to the first gestures of an alternative theory.
The idealism section, as Sassen builds it, reads like a dialectical spiral. Feder reframes his concern after the Prolegomena: the issue is less Berkeley and more the status of appearances. If space and time are subjective, and if the only immediate objects are representations, can one still warrant the assertion of extra-mental things? Feder’s strategy is to retrieve a common-sense realism adjusted by distinctions between primary and secondary qualities and between acts and objects of perception. The belief in an external thing, he suggests, arrives as a nondemonstrative but basic judgment—neither a picture in the mind nor an inference licensed by a category’s extension beyond experience. Sassen’s presentation of this maneuver stresses a double edge: Feder concedes representational mediation yet resists the Kantian narrowing of warrant to transcendental grounds, installing instead a phenomenology of immediate assent—axiomatic in status—that Kant’s framework has no easy place to house. The argumentative pressure reappears, later, as a call to refutation of idealism that will be recast in the B-edition.
Schaumann’s “letter” to Feder—subjected to a critique of the Aesthetic—functions, in Sassen’s design, as a didactic prism. He takes Kant to secure a reality/imaginary distinction through sensation and to win space for an inference to a transcendent cause of sensation. In doing so he unintentionally confirms Jacobi’s charge: any causal traffic appealed to in favor of things in themselves oversteps the very strictures Kant had set. Sassen’s editorial choice to place Schaumann before Jacobi compresses an instructive sequence: an apologetic construal of Kant invites, and then is arrested by, a radical critique that exposes the cost of that very construal. Feder’s measured realism, Schaumann’s representationalist exegesis, and Jacobi’s unwavering attack triangulate a problem set that the Refutation of Idealism will be written to meet. The effect is historical without being antiquarian: one sees the B-edition as the internalization of these pressures, less a polemic against putative “misreaders” than a belated learning from them.
Sassen’s final large cluster addresses the Categories, where empiricists test the table’s source, scope, and necessity. Selle’s stark thesis—there are no concepts of reason independent of experience—presses hard on two Kantian joints: the epistemic status of the principle of non-contradiction and the alleged need for non-empirical concepts in synthetic judgments. By treating even analytic necessity as an induction from the habits of sound minds, he replaces transcendental grounding with generalized psychological regularity. Tiedemann’s continuation against the Analytic and Tittel’s probing of forms of thought refine the same gambit: accuse Kant’s table of being assembled by analogy and association rather than read off from the understanding’s immanent self-legislation, and treat Kant’s architectonic as overlay rather than discovery. The power of Sassen’s curation here is diagnostic. Read together, these pieces show how the empiricist flank redefends metaphysics as disciplined probability, arraigning any appeal to the a priori as a refusal of probabilistic truth-conduct. In that light, the Kantian insistence on apodicticity appears not sublime but evasive—a refusal to admit what kind of certainty metaphysics can actually have.
Throughout, Sassen’s introduction does more than preview contents; it supplies a compositional logic for the book as a whole. The opening survey sets an external frame: journals and publics, the swing from suspicion to partial endorsement, the rise of pro-Kantian venues such as the Allgemeine Literatur-Zeitung, and the broader triadic map of reception. Inside that frame, each section operates as a micrologic of pressure and reply: first, the empiricist fixes the point of leverage (e.g., arbitrariness of synthesis, subjective form of space, genealogies of concepts), then a Kantian defender offers a reconstruction that inadvertently exposes a second vulnerability (e.g., appeal to sensation to mark reality, a causal inference that trespasses the boundary), and finally a more radical critic like Jacobi or a method-shifting figure like Pistorius forces the dilemma to closure. The editorial timing is exacting: pieces from 1782 to 1789 are read as a composition sequence culminating in the year that also marks the other front’s intensification (Eberhard’s Philosophisches Magazin), with Sassen explicitly choosing to stop where the empiricist dossier still bears directly on the shape of the theoretical philosophy before the scene fractures into later disputes.
Two features of Sassen’s method deserve underscoring because they determine the kind of understanding this volume enables. First, the editorial neutrality is principled rather than passive. The introduction isolates claims and argumentative routes, and it marks, without overinterpreting, where Kant responds explicitly and where he declines to do so. This is essential to seeing how empiricist objections do their work—not as confusions swept aside by ex cathedra correction, but as disciplined questions that the Critique itself invites and then fails to close. The result is a portrait of early reception as co-authoring the subsequent Kantian text. Second, the translations are selected, not exhaustive, but the selections are motivated by “firsts”: first review(s), first deployment of the neglected alternative, first explicit challenge to syntheticity in arithmetic and geometry, and so on. These “firsts” identify not only chronology but generative points—sites where an objection first learns its own force and hence where Kant had to learn his counter.
From the perspective of the inner dynamics of the Critique, three thematic through-lines congeal across sections and are then displaced by the emergent demands they generate. The first is determinacy of synthesis: empiricist readers ask what in sensation directs the understanding’s combinatory work so that a unique world-order results. The early dossier leaves the Kantian answer largely promissory unless the schematism is made to carry that determinacy; Sassen notes how little the empiricists engage schematism, which suggests that this most Kantian of mechanisms is not yet rhetorically available to them as a source of guidance. Perhaps that absence itself contributes to the image of an untethered synthesis that makes the illusion/reality distinction unstable. The second is status of space/time: once the a priori is heard psychologically, the very transcendental argumentation risks being misframed, while Pistorius’s hybrid proposal demonstrates an alternative path that grants subjective form and objective accord, at the price of a suspected “lucky fit.” The third is reach of the categories: if their table is not seen as primordially legislative but as retrospectively collated, the transcendental deduction loses necessity and the entire edifice becomes a sophisticated taxonomy of habits. In Sassen’s narrative weave, each through-line tightens the next: indeterminacy of synthesis prompts recourse to form of intuition; the pressure on form prompts recourse to categories; pressure on their origin boomerangs to the initial question—how objectivity, on this picture, avoids arbitrariness.
Sassen’s book thereby stages a method-oriented historiography. It is less a record of “what they thought about Kant” than a display of how particular argumentative styles—empiricist evidentialism, common-sense axioms of perception, hybrid metaphysics—transform the very shape of questions posed to a text. The Feder/Garve dossier is exemplary. The notorious “higher idealism” tag seems, under Sassen’s eye, less an imputing of Berkeley and more a rhetorical grenade that marks impatience with any theory that appears to detach truth from sensation-guided combination. Kant answers by differentiating his transcendental idealism and by invoking the a priori as the law of possible experience, but because this reply does not speak to the guidance question, it misses its target while winning its skirmish. The empiricist counter-moves then travel into the Aesthetic and onward to idealism, where Jacobi exposes the price of importing causality across the boundary. It is in this migration—objection shifting terrain—that one sees, with unusual clarity, how Kant’s theoretical philosophy is pressured into its B-edition re-articulations.
At the level of scholarly apparatus, Sassen’s design cultivates a pedagogical clarity that is itself an argument: she supplies the abbreviations and bibliographical anchors that orient a reader within the late-eighteenth-century periodical economy (most notably the Allgemeine deutsche Bibliothek and the Allgemeine Literatur-Zeitung), emphasizing how journals did not merely transmit debate but structured it. By reminding us that the ALZ soon took on the role of Kant’s defender while Nicolai’s AdB became the forum for criticism, she ensures that the polemical temperature of the period can be felt, not merely described. The book’s closing paratexts (biographical sketches, glossary, bibliography) support this sensibility: they are not neutral ornaments but aids to reconstructing how arguments circulated and accrued authority.
What, finally, does one understand about Kant by reading Sassen’s volume itself—without importing later systematics? First, that early empiricist criticism enacts a disciplined worry about how rather than a skeptical dismissal of that: the question is by what right the understanding’s forms decide objectivity. Second, that Kant’s initial rhetoric—especially as perceived through the A-edition and the Prolegomena—did not give his readers a publicly intelligible route from subjective form to objective lawfulness without either psychologizing the a priori or smuggling causal contact across the boundary. Third, that ingenious alternatives—Pistorius’s chief among them—expose options Kant declined, and thus bring into focus what the Kantian turn costs and buys: it buys the right to necessity at the price of a narrowed conception of evidence; it costs access to things as they are at the price of a demanding account of objectivity that must be earned from within appearances alone. Sassen’s act of editorial construction does not “solve” this balance; it places in our hands the sequence of moves by which the balance was first struck, unsettled, and redressed.
The closing clarification is straightforward. This volume renders a decisive service to Kant scholarship by making accessible, in English, the empiricist repertoire that taught Kant’s theoretical philosophy its earliest public lessons, and by situating those lessons in a compositionally tight time-window where their pressure mattered most. Its value is doubled by its restraint: it distinguishes what is textually secured—dates, venues, contents of reviews, the explicit lines of objection and response—from what is inferential: the reconstruction of argumentative tropes, the charting of how one problem migrates to the next, the suggestion that the B-edition’s recalibrations are in part learned from this very exchange. Read as Sassen asks us to read, the early empiricist critics are not foils to a foregone triumph; they are the first rigorous co-authors of the Critique’s second self-understanding.
Simon Gros 
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