Nietzsche’s “Sensualism” from 1885 to 1888

I The Argument of BGE 15

Nietzsche’s conviction that we are irredeemably caught in the “Lug und Trug” of sensation and of the intellect (D 117) has two sources: his early and never modified belief that the world, ultimately, is Heraclitean flux and that we, in order to secure survival as organisms, have to impose, through our senses and our intellect, a certain degree of order and stability on this reality. This belief was also, at least in the early Nietzsche, confirmed by the problems philosophers in the Kantian tradition had in defending themselves against the complaint that the unknowability of things in themselves leads to skepticism, that is, the complaint that what we call knowledge is only about a scheinbare, not the real world. The Kantians of the 1790s had fought this fight against Kant’s critics, and the Neo-Kantians in the second half of the nineteenth century still had to deal with the same issues. Although a card-carrying Kantian should not admit that what we know about the world of appearances is a falsification of the world of noumena, the incautious reception of the results of the physiology of the senses by Neo-Kantians – most importantly for Nietzsche, by Lange and in an anticipatory way by Schopenhauer^[10] – could only compound the difficulties. The opposed realist view asserted that we have knowledge of a mind-independent material world, that is, in Kantian terms, of things as they are in themselves. Since this external world was usually thought of as constituted by matter, contemporary literature only occasionally kept realism and materialism conceptually apart. (I shall follow this habit here; only later, in section III, the finer distinction will become important.) In his Geschichte des Materialismus, Lange made abundantly clear that materialism, as a heuristic in the practice of science, has been and continues to be fruitful; his main point, however, was that the materialist in the end has to admit that the results of research – not least in the physiology of the senses – require an idealist view. The materialist’s matter, with all its properties, has to be regarded as a representation, a mere appearance, in our mind because these properties themselves are the product of our “Empfindungsmechanismus,” that is, the physiology of our sense organs.^[11]

In BGE 15 Nietzsche puts his finger on this issue:

In order to pursue physiology with a good conscience, one has to insist that the sense organs are not appearances in the sense of idealist philosophy: as appearances they could not possibly be causes! Sensualism, therefore, at least as a regulative hypothesis, certainly as a heuristic principle. – What? And others even claim that the external world is the product of our organs? But then our body, as a part of the external world, would be the product of our organs! But then our organs themselves would be – the product of our organs! This is, it seems to me, a complete reductio ad absurdum: supposing that the notion of a causa sui is a complete absurdity. Hence the external world is not the product of our organs –? (BGE 15)

The project of a physiology of the senses was to investigate causal relations: how external objects affect the sense organs and how they, in turn, give rise to our representations of the external world. Ignoring the second part of the text (starting with “What?”) for now, Nietzsche’s lapidary statement that appearances cannot be causes is mysterious because, for the idealist, causation is a relation only between appearances. Surely, Nietzsche was aware of this and, for instance, critically remarked on attempts to infer from appearances to things in themselves as their cause (e.g., HH I 16). What could he have in mind with this statement, which, if true, would indeed be an obstacle for doing physiology?

Nietzsche’s argument for the claim about the causal impotence of appearances is actually given in the second part of BGE 15. In fact, the issue he raises here for the idealist is an old problem that had been discussed by critics of transcendental idealism since Friedrich Heinrich Jacobi first brought it up in 1787: the problem of “empirical affection,” which was among the problems that motivated Kant’s critics in the 1790s, who accused him of skepticism.^[12] The problem in its general form is this: objects of experience are appearances, that is, on a popular understanding of Kant, they are representations in the mind. The table in front of me is nothing but the table-wise representation I have. If this is granted, then it is paradoxical that this empirical object, the table, should be able to causally affect me so that I have those representations, which, after all, are precisely those that constitute the empirical object. How could the very representations that constitute the table at the same time cause me to have these representations? If x constitutes y, y cannot be a (or the) cause of x. Nietzsche poses this general problem for the special case of sense organs in the second part of the text. To make the difficulty for the idealist more vivid, he adds that if x constitutes y, then y could only be the cause of x if we allow x to be a causa sui, a supposed absurdity. This reductio establishes the claim that objects, as appearances or representations, cannot be causes.

The transcendental idealist might object that Kant’s notions of appearance and representation have been misunderstood in setting up the causa sui argument. Nietzsche confuses an empirical or psychological concept of representation with the transcendental notion Kant employs, where the former merely designates a state of mind while the latter always contains a reference to things as they are in themselves.^[13] It is indeed interesting that these things are left out of Nietzsche’s discussion^[14] – in contrast, for instance, to many places in Lange where he emphasizes that sense organs (and the brain) are nothing but representations but that they are always appearances of unknowable things in themselves.^[15] On this view then, the empirical objects are “mere” appearances but they are not fully constituted by their representations; they have a “ground” in the noumenal, mind-independent world. How this “grounding” is to be understood is, of course, a major problem since it is officially ruled out that appearances are caused by things in themselves.

In his Grundriss der Geschichte der Philosophie, one of Nietzsche’s standard references in the history of philosophy, Ueberweg gave a formulation of the problem that comes close to Nietzsche’s own. But Ueberweg made clear that he thought that the difficulty arises only for idealists like Sigismund Beck, who tried to eliminate things in themselves:

Beck eliminates the question about the origin of the empirical matter of representations by assuming an affection of the senses by appearances (since the appearances themselves are only representations, however, this assumption involves the absurdity that the origin of our representations in general is conditioned by the effect of our representations on our senses, that is, that our representations affect us before they exist.^[16]

The attempt to hold on to noumenal causation, or grounding of appearances by things in themselves, while also allowing empirical affection (appearances cause representations) led Hans Vaihinger in 1884 to propose the doctrine of “double affection,”^[17] which he later however found contradictory as well.^[18]

The problem of the causation of appearances by things in themselves thus remained an unresolved difficulty for the Neo-Kantians, although it was not often diagnosed as openly and succinctly as in Vaihinger’s publications. The Neo-Kantians of his time, Vaihinger summarized resignedly, largely repeated the development of thought about this issue that exercised the Kantians of the 1790s, without having made substantial progress in a hundred years.^[19] Meanwhile, physiologists and Kant sympathizers like Hermann von Helmholtz apparently practiced their trade without a bad conscience, readily admitting ignorance about things in themselves but invoking them in (more or less) cautious ways for explaining certain structures in our perceptions. Helmholtz sketched the framework of his sense-physiological investigations in this way: When we assume that perceptions occur in our mind according to causal laws, we can infer that when we experience different perceptions, they originate under different “reale Bedingungen” that must have occasioned the perceptions. About these conditions themselves, about the “eigentlich Reale” that is the basis of the appearances, we know nothing.^[20]

In light of the argument in BGE 15, Helmholtz should not have been entitled to his good conscience.^[21] Without admitting the “real conditions,” the physiologist’s framework reduces to causation between mere representations. That this is an absurdity, Nietzsche had noted several times before Beyond Good and Evil in his Nachlass. Perhaps the earliest fragment on this issue is from winter 1883/84: “Our sense organs as causes of the external world? But they themselves are just effects of our ‘senses.’ – Our image of the eye is a product of the eye” (Nachlass 1883/84, 24[35], KSA 10.663). In spring 1884, Nietzsche finds Lange’s view contradictory (or “at least indemonstrable”) that the sense organs are merely appearances and effects of our senses. He even labels this view “the coarsest form of idealism” and provides a (surprising) “sufficient proof of the contrary”: since objects, understood as mere representations, cannot cause anything, the fact that we have photographs of objects demonstrates that objects are causally efficacious (Nachlass 1884, 25[310], KSA 11.92).^[22] In the same note, Nietzsche, as it were, stamps his foot and declares: “That tartarus stibiatus makes me vomit, has nothing to do with any ‘appearances’ and ‘opinions’.” This seems to correspond to the claim in a Vorstufe to BGE 15: “Therefore, sensualism as regulative hypothesis: as we have it in life. Nobody regards a beefsteak as an appearance” (KSA 14.350).^[23] Such pronouncements will become important in understanding what Nietzsche might mean by sensualism in BGE 15.

II Sensualism

Lange famously claimed that: “The physiology of the sense-organs is developed or corrected Kantianism, and Kant’s system may, as it were, be regarded as a program for modern discoveries in this field. One of the most successful inquirers, Helmholtz, has employed the views of Kant as a heuristic principle.”^[24] BGE 15 can be read as a direct response to this: Nietzsche argues that, on the contrary, the physiologist cannot use Kant but has to use sensualism as a heuristic (or regulative) principle. But what did Nietzsche mean by this? From the just quoted unpublished notes one might suspect that he had a version of realism or materialism in mind, according to which we take material objects (including the sense organs) in the external world to causally affect us and produce representations. The published text, however, is more cautious: apart from qualifying sensualism as a “regulative hypothesis,” the open question at the end leaves the issue of realism or materialism apparently undecided. Furthermore, a regulative principle in the Kantian tradition is a (transcendentally motivated) maxim for research that entitles one to treat a domain of objects “as if” they had certain properties, or “as if” they stood under certain laws. From such a maxim one is not entitled to assert as true that the objects indeed have such properties, etc. This qualification should be kept in mind in interpreting BGE 15, as well as the conditional phrasing (“if you want to do physiology”) – two reminders that the text cannot straightforwardly be taken to express Nietzsche’s own view.^[25]

It has been suggested that the notion of sensualism relevant for BGE 15 is an epistemic one, not an ontological one. Maudemarie Clark and David Dudrick spell out the epistemic version as the view that “the senses are the only source of information or evidence” or (equivalently?) that “the senses are causal conditions of knowledge.”^[26] The ontological version, by contrast, takes sense perception as the criterion of reality: “only what is in principle sensible is real.”^[27] I shall adopt this distinction in the following, although the limitations of its applicability will become clear as I proceed.

At least the first of the epistemic formulations is uncontroversial and has been widely used in the nineteenth century. According to Heinrich Czolbe, the most prominent self-declared sensualist in Germany of the time, sensualism has to show “how perceptions, representations, concepts, judgments, inferences, the will etc. develop alone from the senses.”^[28] In their discussions of Czolbe’s program, Hermann Lotze and, following him, Lange emphasized that sensualism, so characterized, is, in principle, neutral with respect to realism (or materialism) and idealism.^[29] For the “strict” sensualist, they point out, it is of no concern whether sensations are caused by other representations (as idealism holds) or by matter, that is, mind-independent objects (as the materialist holds).^[30] Czolbe, however, presents his position as a materialist, anti-idealist view.^[31] The transformation of the apparently metaphysically neutral position into a metaphysical one comes about because he added a methodological postulate to the strict version of sensualism: he insisted that only “visualizable concepts” (anschauliche Begriffe) must be admitted in the construction of a philosophical theory,^[32] an addition that is not obviously implied by the strict version. The postulate is for Czolbe in practice satisfied only by mechanistic accounts of how representations are formed on the basis of external stimuli, how self-consciousness arises, etc.^[33] By requiring Anschaulichkeit in this sense, he uses sensualism, as Lange says, “as a regulative principle, while the metaphysical principle is matter.”^[34]

Czolbe thus abandons the metaphysical neutrality of “strict” sensualism by imposing the requirement that the development of representations out of sense impressions be explained in a visualizable, that is, mechanistic way. Materialism is the result. In BGE 15, Nietzsche, by contrast, eliminates idealism as a metaphysical option for the physiologist and arrives at the recommendation of sensualism. On account of the elimination of one of the two metaphysical alternatives, the Nietzschean sensualist would seem to be committed to materialism. With idealism rejected, epistemic sensualism cannot remain neutral.^[35] As a regulative hypothesis it should now be understood as the recommendation to treat the sense organs (and the external world generally) as if they were causally efficacious material objects. Since regulative principles do not assert anything about the world but merely ask us to treat the world as if it were such and such, there is no commitment to materialism involved – hence Nietzsche’s ambivalent or tentative concluding question.

There is, of course, something unsatisfactory about such a position. But the understanding of sensualism and materialism as regulative hypotheses is, I think, as much as one can responsibly attribute to Nietzsche. It should be emphasized though that the sensualism he seems to recommend cannot be the “strict,” metaphysically neutral sensualism of Lotze, Fischer, and Lange; nor can it be Clark and Dudrick’s “epistemic sensualism” if “epistemic” were to be understood as involving no metaphysical commitment. If Nietzsche is right, sensualism involves realism or materialism, in the form of a regulative hypothesis.

It is well known that in the Nachlass he often classified mechanism and atomism as useful views in the scientist’s toolbox – with caveats, of course. In spring of 1884, the “method of the mechanical world view is so far the most honest method” (Nachlass 1884, 25[448], KSA 11.132), and a year later: “the mechanistic [world interpretation] today seems to stand triumphantly in the foreground: clearly it has good conscience [!] on its side” (Nachlass 1885, 36[34], KSA 11.564). The caveats are noted at the same time: “the mechanistic notion of pressure and thrust is only a hypothesis on the basis of Augenschein and the sense of touch, although it may serve us as a regulative hypothesis for the world of Augenschein!” (Nachlass 1885, 34[247], KSA 11.504).

The term Augenschein in such passages is obviously meant critically. It has connotations of superficiality and illusion; the mechanistic world view is therefore a “Vordergrunds-Philosophie.”^[36] It is Augenschein that tells us: the earth does not move (BGE 10). And the often-quoted aphorism: “All credibility comes from the senses in the first place, all good conscience, all Augenschein of truth” (BGE 134) should be read with the same critical flavor of Augenschein in mind that is expressed in the claim that: “The law of identity [which Nietzsche rejects] has as its background the ‘Augenschein’ that there are equal [gleiche] things” (Nachlass 1885, 36[23], KSA 11.561). This is made perfectly clear when Nietzsche calls Copernicus and Boscovich “the greatest and most victorious enem[ies] of Augenschein” and explains that Boscovich’s theory of “dynamic atoms” or “centers of force” was the “greatest triumph over the senses that has been achieved so far on earth” (BGE 12). The praise for Copernicus is implicitly repeated in Twilight of the Idols: the “error” we commit when we take the sun to be moving rather than the earth has “our eye […] as its perennial advocate” (TI, Reason 5). This advocate, which Copernicus defeated, must be Augenschein rather than the “testimony of the senses,” the acceptance of which is supposedly the necessary condition for science (TI, Reason 3).

Mechanistic atomism is suitable for the world of Augenschein – even though the atoms are, of course, invisible – because the atoms are imagined to be miniature versions of tangible bodies and hence “in principle” sensible objects.^[37] Sensualism in this sense might seem to be a criterion of reality along the lines of Clark and Dudrick’s ontological sensualism. But a refinement has to be made here: “in principle sensible” translates into the requirement that the entities postulated by the theories, and thereby the theories, should be anschaulich. This is a methodological maxim, a criterion not of reality but of intelligibility. With the possible exception of Czolbe, it was used as such by Lange and by many eminent physicists at the time.^[38] According to Lange (who even attempted something like a transcendental deduction of the maxim),^[39] we do not understand – that is, find intelligible – any theory unless it operates with anschauliche hypotheses. But nothing is thereby decided about the reality of the entities the hypotheses postulate. Lange thus has no objections to using forces and action at a distance in physics, although the former are “unsinnlich” and the latter is “transcendent” or unintelligible. The criterion of intelligibility, Lange points out, is a main reason for the success of atomic theories.^[40] But he clearly did not support ontological sensualism in Clark and Dudrick’s sense.

Although he recommends mechanistic atomism as a heuristic for the world of Augenschein, Nietzsche also has reservations, which he articulates, for instance, in BGE 14. Anschauliche theories, of material atoms, e.g., encourage the application of the “Wahrheits-Kanon of the eternally popular sensualism,” the “sensualist coarse prejudice,”^[41] namely, to (mis)understand the methodological maxim as a criterion of reality (that is, in the sense of ontological sensualism) or as a much too narrow criterion of intelligibility. In order to discourage the prejudice, it is desirable to formulate theories that avoid Anschaulichkeit – and thereby can triumph over Augenschein. Boscovich’s system of force centers accomplished precisely this by rejecting the assumption of the “Klümpchen-Atom” (BGE 12) in favor of the point atom that cannot, even in principle, be visible or touchable. Boscovich himself emphasized this feature of his proposal, which was, of course, not motivated by concerns about Anschaulichkeit but by mathematical difficulties in the treatment of inelastic collisions of extended atoms:

for the purpose of forming an idea of a point that is indivisible and non-extended, we cannot consider the ideas that we derive directly from the senses; but we must form our own idea of it by reflection […]. [Of this idea], using only the equipment that we have got together for ourselves by means of the senses from our infancy, we could not have formed any conception.^[42]

For Nietzsche, this remoteness of the postulates of a theory from the senses is a tool in overcoming Augenschein. While the “eternally popular sensualism,” understood in the ontological sense, displays a “plebeian basic taste” and finds in “that which can be seen and touched”^[43] the suitable tool to perform the “coarse work” of a “coarse industrious race of machinists and bridge builders,” a “noble way of thinking” characterizes the anti-sensualist, the Platonist idealist: “precisely in the resistance against what falls into the senses [Sinnenfälligkeit] consisted the charm of the Platonic way of thinking, which was a noble way of thinking” (BGE 14).^[44] Although Boscovich had of course nothing to do with idealism, it is easy to see some of this nobility, the “pathos of distance” from the senses (BGE 257), in his abstract theory that does not provoke the sensualist prejudice of the workers engaged in pursuing coarse tasks.

In a letter to Köselitz from late August 1883, Nietzsche emphasized that Boscovich’s theory is “useless” for “practical applications” of science (no. 460, KSB 6.442); it does not assist the “machinists and bridge builders of the future,” for which the “imperative” may be suitable that “[w]here humans have nothing more to see and to touch, there they also have nothing more to investigate” (BGE 14). By contrast, Nietzsche’s view of Boscovich’s achievement is well characterized in Lange’s comparison of “idealist” and “materialist” researchers. The idealist scientist’s work “often […] stands in direct opposition [Widerspruch] to the testimony of the senses and of our understanding” – while

materialism […] suffers from a comfortable satisfaction with the world of appearances […]. The urge to go beyond the apparent objectivity of the sensible appearances is missing, as is the urge to extract a completely new language from the things through asking paradoxical questions and to design experiments that […] explode the customary view of the world […]. Materialism in the natural sciences is, in one word, conservative.^[45]

I shall come back to this characterization in the next section. For now, it remains to point out that BGE 14 classifies the “physiological workers” together with the engineers and others who are engaged in performing coarse tasks. According to Clark and Dudrick, Nietzsche unreservedly sides with these researchers – the ones who rely on the sensualist prejudice.^[46] In light of his criticism of the prejudice, this seems quite implausible, however important their work might be for the “future.” In fact, Nietzsche’s reservations carry over into BGE 15, where he recommends sensualism as a heuristic to physiologists.^[47] One could say that Nietzsche’s complaint against “the eternally popular sensualism” in BGE 14 is in fact a criticism directed against those who mistake a regulative or heuristic hypothesis for a true assertion about the world.

Riccardi agrees that BGE 15 seems to recommend a kind of materialism (of mind-independent objects).^[48] But the previous section, he thinks, rules this out: Nietzsche rejects this materialism or “folk sensualism,” partly because he does not want to bring back a view that has already been eliminated by Schopenhauer and Lange. Instead, Riccardi attributes to Nietzsche a “qualified sensualism” that treats sense organs as collections of force centers that interact with other force centers in the “external world.” As plausible as this interpretation looks in light of Nietzsche’s “power ontology,” it overlooks the qualifier “regulative” in BGE 15. Nietzsche indeed rejects “folk sensualism” as a misunderstanding of regulative hypotheses as assertions about the world, a misunderstanding encouraged by Anschaulichkeit. But as long as the hypotheses are understood as regulative – that is, as I shall discuss in section III, as “interpretations” rather than “explanations” – folk sensualism is a suitable heuristic for the world of Augenschein. There is, however, a better or “nobler” alternative (though not necessarily for practical applications of science): the immaterialist mechanism of Boscovich, which allows the scientist to triumph over Augenschein, while still accepting the testimony of the senses. Insofar as this mechanistic theory replaces material atoms with extensionless force centers, accepting Boscovich’s view implies that the late nineteenth-century convention of equating realism with materialism has to be given up. Nietzsche’s regulative sensualism that implies the rejection of idealism, it turns out, does not imply materialism but “merely” realism: the realism of Boscovich’s matter-less world.

III Explanation

The skeptical characterization of the “physiological workers” in BGE 14 is prefaced by Nietzsche’s complaint that those who adhere to “popular sensualism” tend to mistake theories in physics for “explanations” of the world, while in fact – recognized only by a few contemporary minds – they are merely different “interpretations” (Auslegungen) of the world. The misunderstanding, as we have seen, is, according to Nietzsche, encouraged by the theories’ Anschaulichkeit: accounts of phenomena that are couched in terms of anschauliche entities (like material atoms) are easily taken as explanations, that is, as giving us a true causal story. One might think that the misunderstanding could at once be corrected when we regard, with Nietzsche, such theories as merely regulative hypotheses. After all, Kant had insisted that on the basis of such hypotheses no proper – for Kant, mechanical – explanations can be given. We assume, for instance, that organisms are “natural purposes,” that is, we assume them to be organized according to a purpose; but since there are no literal purposes in nature, no true causal stories can be derived from the regulative supposition. Although this view could account for Nietzsche’s regarding theories even in physics as interpretations rather than explanations, he does not explicitly spell out his claim in these terms.

His skepticism about the ability of physics to provide such explanations, however, can be traced in earlier publications (e.g., GS 112) and in numerous places in the Nachlass. It is also not an attitude that is idiosyncratic to him. It can be found in scientists’ pronouncements of the time and in Lange, who noted that “most of today’s ‘materialists’ […] are essentially skeptics; they do not believe anymore that matter, as it appears to our senses, contains the ultimate solution of all the riddles of nature; yet they proceed in principle as if it were so.”^[49] In much the same terms Nietzsche himself diagnosed a development in science towards a “sovereign ignorance” (Nachlass 1886/87, 5[14], KSA 12.189). His claim in BGE 14 that only “five or six minds” had realized that physics is dealing with interpretations, not explanations, therefore is somewhat exaggerated. But his skepticism about explanation fits smoothly into this context.

Clark and Dudrick, however, have tried to rescue Nietzsche from the apparent skepticism and offered a reading of BGE 14, according to which Nietzsche himself did not let go of the image of physics as providing us with explanations (albeit of a Humean kind).^[50] The availability of theories that explain the world differently than materialist atomism – namely, the availability of an immaterialist theory like Boscovich’s – Clark and Dudrick claim, has confused people into believing that physics gives us only different interpretations of the world. This confusion is to be blamed on ontological sensualism, the mistaken view that a theory’s Anschaulichkeit is an indication of its truth and its ability to give us true explanations of the world. Since Nietzsche rejects ontological sensualism as a prejudice, Clark and Dudrick conclude that he is entitled to the view that physics does explain, while accepting that there can be explanations that are better than others. They find the appropriate contrast in epistemic sensualism, the kind that Nietzsche supposedly embraces in BGE 15.

This extraordinary interpretation of BGE 14, I think, is hard to defend, both on contextual grounds and in light of the evidence of the Nachlass (which, however, is off-limits for Clark and Dudrick). Instead of dwelling on this, I add a further reason for doubting that Nietzsche maintains that physics explains the world. His general and often repeated view of explanation is neutral with respect to truth: explanations reduce the unfamiliar to what we are familiar with; such reduction gives us the feeling that we have understood something.^[51] It seems clear, however, that he regards this sort of explanations critically, even though he can account for it in terms of securing the survival of the species. What could be objectionable to this explanatory practice and motivate skepticism? In a famous and widely discussed speech on The Limits of Our Knowledge of Nature (1872), the eminent physiologist Emil du Bois-Reymond proposed a reason.^[52] Our desire for explanations, he said, cannot ever be satisfied by atomistic mechanism; all that it delivers is “only a sort of substitute for an explanation.” This is because these theories “in fact, carry over into the region of the minute and invisible the concepts we obtained in the region of the gross and visible.”^[53] Thus, the very advantage that Lange saw in the Anschaulichkeit of atomism is turned by du Bois-Reymond into the claim that such atomistic theories abdicate the task of giving satisfactory explanations because they try to account for the unfamiliar and invisible in terms of what we are familiar with.^[54] Nietzsche saw this problem with “explanation” in a similar way: “To trace an unfamiliar thing back to things we are already familiar with, to get rid of the feeling of strangeness – that counts for our feeling as explaining. We do not want to ‘know’ [erkennen]; we rather do not want to be disturbed in our belief that we already know [wissen]” (Nachlass 1885, 34[246], KSA 11.502–3).

Although scientists, according to Nietzsche, “instinctively” aim at explanation in the sense of reducing the unfamiliar to the familiar, their practice shows that what actually has recently happened is the reverse; the theories dissolve the known into the unknown (Nachlass 1886/87, 5[14], KSA 12.189). Boscovich again is an illustration, although Nietzsche does not mention him in this fragment. Because his theory does not reduce the unfamiliar to what we know, i.e., because he does not give explanations in this sense, he reveals to Nietzsche that the business of physics is actually to give interpretations instead of explanations.^[55]

In sum: the Anschaulichkeit of materialist mechanistic theories tempts people to regard them as more than regulative hypotheses. This temptation is minimized by Boscovich’s theory, which Nietzsche understands as exemplifying immaterialist or dynamic mechanism. It is an interpretation, rather than explanation, of the world, an interpretation that suggests a “scientific image” of the world, in contrast with the “manifest image,” the world of Augenschein.^[56]

IV The Senses Do Not Lie at All

If Nietzsche did not unambiguously embrace sensualism in Beyond Good and Evil, it becomes a deeper mystery why he seemed to have presented, shortly after 1886, a view that does sound very much like it. We have seen that in Twilight of the Idols he distinguishes between Augenschein and the testimony of the senses and uses the distinction to praise the triumph over the former (in Copernicus, though Boscovich is now not mentioned or alluded to) while maintaining that the senses do not lie and that we have science only to the extent that we have accepted the testimony of the senses (TI, Reason 2 and 3). The world of Augenschein, obviously, is the product of the senses, together with the intellect – a product that is a falsification of the world. This is Nietzsche’s view throughout his career, although what is being falsified in his later opinion is no longer a world of things in themselves but, perhaps, a “chaos of sensations” or a world of centers of force.^[57] In Twilight of the Idols, the senses do not lie, but only “what we make of their testimony injects the lie […]. ‘Reason’ [the intellect] is the cause of our falsification of the testimony of the senses” (TI, Reason 2). The senses are innocent and only reason, with its “categories” of unity, thinghood, substance, permanence is to be blamed. Apart from the accusation of thoroughgoing falsification by reason, this is reminiscent of Kant’s view in the first Critique that what the senses deliver cannot be false because they do not judge at all. Nietzsche’s claim, however, seems to repudiate much of what he had pronounced previously, namely that there is a “double falsification,” from the senses and from the intellect (Nachlass 1886/87, 7[54], KSA 12.312). Since such falsifications are necessary for the survival of the species and have evolved accordingly,^[58] it is surprising that Nietzsche now seems to exempt the senses from this development and only includes the intellect in it. While it is evident that by the time of Twilight of the Idols, he has not given up on the “falsification thesis” or adopted a form of common-sense realism, as Clark once suggested, the re-distribution of blame is striking.

Riccardi has proposed a straightforward answer to the question of what Nietzsche could have meant by “the senses do not lie at all.”^[59] In Twilight of the Idols he must be distinguishing between sensations that are “interpreted” by the intellect according to its categories and “pure” sensations that are not yet touched by such interference. Thus, while in D 117 or GS 110, for instance, Nietzsche still held the comprehensive falsification view, in Twilight of the Idols he has retreated to a selective view. Why this partial change of mind concerning falsification should have occurred, is left open. But Riccardi points out that the distinction was not an innovation of Nietzsche’s; it was widely available to nineteenth-century physiologists.^[60] It had been an ingredient in Helmholtz’s (and other’s) framework^[61] from early on as the distinction between “sensations” and “perceptions,” where the former are the “raw materials” from the sense organs (nerves), upon which intellectual functions operate, unconsciously, to produce perceptions (e.g., representations of three-dimensional objects).^[62] These operations were usually labeled “unconscious inferences” that the mind performs, a form of inductive inferences, whose status and origin remained somewhat vague.^[63] Lange’s reception of this view, which largely follows Helmholtz, culminates in the claim that the eye itself “makes, as it were, a probabilistic inference, an inference from experience, an incomplete induction […]. [I]n this case, seeing itself is an inference and the inference is performed in the form of a visual representation […]. Seeing and inferring are here one and the same.” More explicitly than Helmholtz himself, Lange insisted that he regards it “as methodologically inadmissible to separate in this case [the act of] inferring and [the act of] seeing.”^[64] This sounds as if there cannot be anything like “innocent” sensations; they are too intimately interwoven with intellectual activities.

It is indeed clear to Helmholtz that what is immediately available in consciousness when we have experiences, is not the “raw” but the interpreted material, the full-fletched perceptions of objects, etc., as opposed to single sensations of colour or tactile sensations.^[65] “The knowledge of objects precedes the knowledge of sensations,” Ernst Cassirer summarized Helmholtz’s view; the former is “far superior in clarity and distinctness” than the latter, and we have to make special efforts and learn how “to direct our attention on our particular sensations” in an act of conscious reflection.^[66] The thus isolated sensations – which, to repeat, are not available in immediate experience, i.e., before reflection – Helmholtz treats as “signs” or “symbols” in order to emphasize that, for all we know, they are not “images” that we could expect to resemble their causes in the external world. To even ask the question about such resemblance or correspondence of signs and what they signify does not make sense, he maintains; it would be as misguided as to ask “whether a certain sound is red, yellow, or blue. The representation and what is represented obviously belong to two wholly different worlds, which admit of comparison with each other as little as colours and sounds or as the letters of a book and the sound of the word that the letters indicate.”^[67]

The artificially isolated “pure” sensations, therefore, cannot “falsely represent because they do not represent at all,” as Riccardi sums up what he takes to be Nietzsche’s view.^[68] The “pure” sensations do not give us (in Riccardi’s terminology) pictorial or conceptual content; they are Helmholtzian signs, not images. In this respect, Nietzsche’s sensualism can be regarded as a reliabilist view: “since sensations are causally warranted responses to external stimulation, it makes no sense to say that they falsify reality.” They merely indicate the presence of a stimulus. Falsification, then, “first comes into play only once we have manipulated their [the senses] testimony.”^[69]

The reliability of the senses, according to Riccardi, is thus restricted to “pure” sensations as Helmholtzian signs. He also points out that in order to make sense of the idea of pure sensations, Nietzsche would have to be committed to Helmholtz and Lange’s claim that to “attend to sensory qualities as such […] is usually effortful and unnatural.”^[70] Following this interpretation, we can understand Nietzsche’s earlier claims about falsification by the senses as claims in which he did not yet make the distinction and treated sensations always as interpreted. The “double falsification,” from the senses and from the intellect, could be accounted for along these lines. Riccardi’s proposal also makes sense of Nietzsche’s unusual choice of example in Twilight of the Idols (TI, Reason 3) where he praises the accuracy of our senses in the case of the nose. In the sense of smell, according to Riccardi, we are less likely to find “conceptual paraphernalia,” that is, interpretation of sensations, than in the visual case and find it therefore easier to attend to the sensory qualities themselves.^[71]

But what use could such pure sensations be to science? I am assuming that Nietzsche’s claims that the senses do not lie and that we have science only to the extent we have accepted the testimony of the senses must be connected. Maybe this assumption is misguided. The contrast of Augenschein and testimony of the senses, however, seems to strongly indicate such a connection. But Nietzsche’s admission of pure sensations in Riccardi’s sense – “purely qualitative states of consciousness” – does not elucidate how the two claims might relate to each other.^[72] We can, however, find a clue in the example of the accuracy of olfactory sense perception.

Nietzsche’s analysis of this case emphasizes that the nose is capable of detecting “minimal differences of motion [Bewegung] […] that even the spectroscope does not detect” (TI, Reason 3).^[73] Although it is notoriously difficult to understand why Nietzsche thought smells have anything to do with “motion,”^[74] the point clearly is that the nose is a reliable and accurate detector for even minute changes in the environment. Thus, although olfactory sensations do not represent qualities of objects in the sense in which we attribute the quality of a smell to an object as one of its qualities, they do function as indicators of some “motion” or change when we think of the transition from a neutral olfactory state to, say, becoming conscious of a pleasant smell. Generalizing, one could say, with Nietzsche, that the senses do not lie insofar as they show us change.^[75] And this is what he actually says in Twilight of the Idols when he qualifies “the senses do not lie at all” immediately afterwards as: “insofar as the senses show becoming, passing away, change, they do not lie” (TI, Reason 2). In this passage, Nietzsche observes that Heraclitus was correct in his ontology of flux but mistaken in his rejection of the testimony of the senses. If we trust this testimony insofar as it shows us change, we can say that the senses do not lie and actually provide us with the basis of a science that takes change seriously by eliminating the fiction of unchanging matter. The relations of temporally changing sensations (pure or not) indicate corresponding relations in the external world, even though the sensations themselves cannot be taken to represent objects or qualities.

This view is actually found in Helmholtz^[76] as well: “our sensations [are] only signs of changes in the external world […] and can only have the significance of images in the representation of the temporal sequence” of such signs.^[77] That is, for Helmholtz, only the change, the temporal sequence of sensations, can make a claim to represent (be an image of) changes in the external world; the individual, isolated sensations can make no such claim:

The only respect in which there can be an actual correspondence [Uebereinstimmung] of our perceptions with reality is in the temporal sequence of events […]. Simultaneity, sequence, the regular recurrence of simultaneity or of sequence, can occur in sensations just as in the events. External events, just like their perceptions, happen in time, and, therefore, can the temporal relations among the latter be the correct image of the temporal relations among the former.^[78]

Helmholtz presupposes that perceptions arise in us according to “fixed laws, so that when different perceptions force themselves upon us, we are entitled to infer from this a difference in the real conditions under which they were formed.”^[79] This quasi-transcendental assumption that all changes, in sensations and in the real world, happen in a lawlike way allows Helmholtz to claim that even though individual sensations are merely signs and not images, their lawlike changes, their relations in time, can serve as images of corresponding relations in the real world. Since science, for Helmholtz, aims at discovering the lawfulness of such temporal relations (Zeitverhältnisse), he can come to the optimistic conclusion that “what our sense organs accomplish is just sufficient for fulfilling the task of science and is also sufficient for the practical purposes of the acting human being.”^[80]

This is evidently the view Nietzsche announced in Twilight of the Idols. Although he did not formulate the aim of science in terms of revealing laws of nature and had serious reservations about the very notion of such laws, he too claims that what the testimony of the senses provides us with, is the basis for our having science and that, therefore, what the senses accomplish is what science needs. His presupposition is that the real world is characterized by flux, of which changes in sensation provide us with a more or less coarse-grained image. To this extent, the senses do not falsify or lie.^[81] It is perhaps not altogether far-fetched to recognize in this view a form of “epistemic structural realism,” according to which the aim of science is not knowledge of things but of “the relations between things; outside those relations there is no reality knowable.”^[82] This is a more general claim than the one expressed by Helmholtz’, who restricted the relations in question to temporal ones. But the underlying idea seems to be the same.

The senses then do not lie insofar as they present us with change, that is, with certain temporal relations between sensations. As the case of Helmholtz shows, this reliability in detecting change is of much more obvious significance to science than the existence of “pure” sensations as reliable indicators of external stimuli. Furthermore, the detection of such relations can be reliable, even when the sensations themselves are “manipulated” and thus are lying.

If it is true that Nietzsche (partially) changed his mind about the senses in Twilight of the Idols, what was the reason for this change? I can only offer a speculation. According to Matthew Meyer, Nietzsche had believed since the 1870s that Boscovich’s immaterialist theory is the way to make contact between his conviction about the flux character of the world and science.^[83] He may have gradually realized that this project cannot succeed if he held on to the comprehensive falsification thesis. In order for a theory like Boscovich’s to give us at least approximate insight into a world without matter, swarming with centers of force, Nietzsche perhaps concluded that such a science needs to make some kind of contact – through the senses – with this world, however insufficient (i.e., falsifying) the theory’s conceptual apparatus might otherwise be.^[84] The real world would be the apparent world, unfalsified by the senses but still subject to intellectual falsification, as required by the needs of organisms. Hence it is still true that “precisely the best science is best at keeping us in this simplified, through and through artificial, fabricated, falsified [zurecht gedichteten, zurecht gefälschten] world” (BGE 24).^[85]