The author declares no conflicts of interest regarding the publication of this paper.
Intuitionism serves as a crucial epistemological method within Sidgwick’s philosophical system. Building upon the intuitionist tradition initiated by Butler, Sidgwick distinguished between types of intuition and established criteria for intuitive self-evidence, thereby laying the foundations for the study of intuitionism. Based on intuitionism, Sidgwick constructed a system of self-evident principles, achieving a transition from self-interest to utilitarianism and demonstrating the self-evidence of utilitarianism. However, Sidgwick’s system of intuitionism contains internal tensions arising from its pursuit of self-evidence and the ineffective concept of “non-dissensus”. This invalid “non-dissensus” is centrally embodied in its criterion of self-evidence and profoundly encapsulates the famous “the Dualism of the Practical Reason”, constituting a fundamental characteristic that must be addressed when studying Sidgwick’s intuitionism.
Sidgwick inherited the intuitionist tradition from Butler and others, incorporating German philosophy to conduct a comprehensive examination of intuitionism. In The Methods of Ethics, Sidgwick distinguished three categories of intuitionism, established four criteria for intuitive self-evidence, and proposed a system of self-evident principles grounded in justice, prudence, and reasonable benevolence. This comprehensive intuitionist framework not only laid the groundwork for subsequent intuitionist inquiry, but Sidgwick also leveraged the persuasive power of intuitionist self-evidence to complete the transition argument from self-interest to utilitarianism, thereby demonstrating utilitarianism’s self-evidence. However, much subsequent scholarship has overlooked the flawed “non-dissensus” principle within Sidgwick’s intuitionism. This flaw pervades Sidgwick’s intuitionism, most notably manifesting in the fourth self-evident principle: Non-dissensus. As Sidgwick himself apprehended, this defect carries the risk of “plunging his philosophy into paralysing scepticism”. Moreover, it is implicit within his renowned “The Dualism of the Practical Reason”, constituting a central tension within his intuitionism system that cannot be overlooked.
Critically, the epistemic failure of the “non-dissensus” criterion is the direct cause of the practical conflict inherent in the Dualism of the Practical Reason. The “non-dissensus” criterion requires that a self-evident moral principle must not be denied by competent judges—yet the Dualism of the Practical Reason precisely arises from the irreconcilable disagreement between Rational Egoism (which upholds the self-evidence of prudence) and Utilitarianism (which affirms the self-evidence of reasonable benevolence). Since neither side can be definitively deemed “incompetent” by Sidgwick’s standards, the failure of “non-dissensus” to resolve this disagreement deprives both principles of the epistemic certainty Sidgwick demands. This epistemic deficit translates directly into a practical impasse: when prudence and reasonable benevolence conflict, there is no self-evident principle to arbitrate, as the very criterion meant to validate such principles (non-dissensus) has collapsed. In short, the inability of “non-dissensus” to secure intersubjective agreement on foundational moral principles creates the epistemic vacuum that gives rise to the Dualism of the Practical Reason as an intractable practical dilemma.
During the nineteenth century, intuitionism enjoyed considerable popularity within British moral philosophy communities. Figures preceding Sidgwick, such as Hutchinson and Butler, were prominent proponents of intuitionism. Within moral theory, “intuition” primarily denotes direct cognition distinct from empirical induction and deductive reasoning, with Butler’s theory of “conscience” proving most influential ([
Butler posited that human beings, as moral entities, are essentially complex organisms possessing multiple affections. These affections are arranged according to a hierarchical order, maintaining appropriate proportions and subordinate relationships ([
Butler’s theory of conscience inherits and to some extent revives the Christian tradition, effectively refuting Hobbes’s moral philosophy rooted in self-preservation, with far-reaching influence ([
Sidgwick pointed out, without some fundamental intuition, the utilitarian method cannot maintain logical coherence and harmony. The goal of intuitionism is to trace, along the path of self-love and benevolence, “those moral intuitions which are both recognised by the philosophical community as ultimately valid and which provide the only possible philosophical foundation for utilitarian tenets. so that ‘the Intuitional method rigorously applied yields as its final result the doctrine of pure Universalistic Hedonism, which it is convenient to denote by the single word, Utilitarianism.” (Sidgwick, p. 564)
To establish a more comprehensive intuitionist system, Sidgwick categorised moral intuition into three types: 1. Perceptual intuitionism, 2. Doctrinal intuitionism, 3. Philosophical intuitionism. These three categories exhibit both a progressive relationship of increasing depth and an interwoven, mutually inclusive relationship.
The First Type of Intuitionism: Perceptual Intuitionism. Drawing upon Butler, Sidgwick employs the term “conscience” to denote “the faculty of moral judgement applicable to individual conduct”, asserting that if one were to follow conscience thus understood in every case, there would be no need for universal rules or “scientific ethics” (Sidgwick, pp. 99-100). Sidgwick termed this perspective “perceptual intuitionism” (Sidgwick, p. 102). describing its most extreme form as “super-intuitionism”—the stance that “I would act thus even if the heavens fell” Sidgwick contended that calling this a “method” was strained, as the “procedure” involved consisted solely of a single judgement. He further observes that few would fully embrace perceptual intuitionism, as most recognise their particular intuitive judgements as “susceptible to doubt, incomplete, inconsistent over time, and frequently in conflict with others’ intuitions.” ([
In the chapter on Ethical Judgements, Sidgwick adds that “the moral faculty relates to individual conduct” is a fundamental commonplace, and that this faculty is closer to “moral sense” than to “rational intuition” ([
Given that perceptual intuitionism centres on “particular actions”, it might be more apt to term it “action-centred intuitionism”. Accordingly, Sidgwick did not distinguish the next “stage” of intuitionism based on some novel moral faculty, but instead opted to make the subsequent distinction based on the object of the moral sense faculty—namely, “moral principles”.
The second type of intuitionism: dogmatic intuitionism. This constitutes Sidgwick’s response to the “defects of perceptual intuitionism” ([
Sidgwick’s legal analogy, while illuminating the structure of dogmatic intuitionism, also reveals its fatal limitation: legal reasoning inherently fails to provide the foundational, self-evident principles Sidgwick requires for moral certainty. Legal rules are conventional, positivist constructs—they derive their authority from legislative enactment, judicial precedent, or social consensus, not from inherent self-evidence. For example, a law prohibiting theft is binding because it is enforced by the state, not because the prohibition itself is intuitively self-evident to all rational agents. In contrast, Sidgwick’s project demands moral principles that are objectively self-evident, transcending convention and capable of resolving all moral conflicts with certainty. Legal reasoning, however, operates within a framework of contingent rules that are often vague, contradictory, or context-dependent—precisely the flaws Sidgwick criticises in common-sense morality. Even a well-systematised legal code lacks the epistemic foundation, Sidgwick seeks: it cannot explain its rules are binding, only that they are enforced. This is the core failure of the legal analogy for dogmatic intuitionism: legal reasoning can classify actions as “lawful” or “unlawful” within a given system, but it cannot validate the system itself as self-evident—something Sidgwick deems essential for moral certainty. Dogmatic intuitionism, by modelling itself on legal reasoning, thus inherits this conventionality, leaving it unable to provide the foundational principles Sidgwick requires.
According to dogmatic intuitionism, universal moral rules are implicit in common-sense morality, and the philosopher’s task is to elucidate these rules and systematise them as far as possible. The importance of this is again illustrated by the legal analogy: if a person is to bear an obligation (whether legal or moral), they should clearly know the content of that obligation when making decisions. An ambiguous law is a bad law; an ambiguous moral principle is a bad principle. ([
Thus, dogmatic intuitionism is not entirely devoid of reflection; indeed, it arises precisely from reflection upon “common-sense beliefs (dogmas)”. Yet Sidgwick deemed this intuitive approach still inadequate, chiefly because he considered it insufficiently reflective to furnish common-sense morality itself with a foundation enabling subjects to ascertain their obligations in particular situations. Sidgwick’s principal objection to dogmatic intuitionism lies not in its “origin in common-sense morality”, but in its cessation at common-sense morality, lacking the precision of a legal system.
Sidgwick implies that those satisfied with common-sense morality lack a “philosophical mind”, for even if such morality maintains internal consistency, comprehensiveness, and answers nearly all practical questions, the resulting principles remain “a fortuitous collection of precepts”. They urgently require rational evaluation, so those with a philosophical mind must inevitably question the universal authority of common-sense moral systems. Hence a third form of intuitionism is necessary: philosophical intuitionism. Philosophical intuitionism precisely arises from dissatisfaction with Sidgwick’s common-sense ethics ([
Though dogmatic intuitionists might argue their theories already provide such depth—claiming, for instance, that betrayal is wrong because it is wrong in itself, or because it is unjust; that helping others is good because it is good in itself, or because it is reasonable and benevolent—Sidgwick deemed such theories unacceptable “unsystematic” products. What he sought was “one or more absolute and undeniably true, self-evident principles” from which one could derive the present moral rules, whether in the form accepted by common sense or with slight modifications and amendments.
It may be observed that Sidgwick actually raises two issues concerning dogmatic intuitionism: the first is that the rules of common-sense morality cannot in practice be sufficiently clear, consistent, comprehensive, or decisive; the second is that even if these rules could be so, they still lack a “background principle (or principles)”—that is, some foundational principle capable of explaining and justifying the rules, thereby demonstrating that they are not merely “accidental”.
Sidgwick devotes considerable attention to the first question but offers only scant discussion of the second. The significance of this issue lies in the fact that the argument against dogmatic intuitionism relies heavily upon his detailed critique in Volume 3. Dogmatic intuitionists, however, could counter many of these criticisms by introducing a sufficiently developed concept of “practical judgement”. Even with such a concept, Sidgwick could still maintain that “dogmatic intuitionism is unsystematic”. The difficulty, however, is that The Method of Ethics here offers only assertions and extensive discussion of common-sense morality. While this reflects Sidgwick’s consistent emphasis on common-sense morality, it lacks the use of typical cases to demonstrate in what sense reflexive dogmatic intuitionism fails to provide such systematic synthesis.
Following extensive detailed exposition on common-sense morality, Sidgwick concludes that even in its most perfected form, it cannot furnish clarity and certainty. He thus reiterates his emphasis on philosophical intuitionism:
“[W]e conceive it as the aim of a philosopher, as such, to do somewhat more than define and formulate the common moral opinions of mankind. His function is to tell men what they ought to think, rather than what they do think: he is expected to transcend Common Sense in his premises, and is allowed a certain divergence from Common Sense in his conclusions. It is true that the limits of this deviation are firmly, though indefinitely, fixed: the truth of a philosopher’s premises will always be tested by the acceptability of his conclusions: if in any important point he be found in flagrant conflict with common opinion, his method is likely to be declared invalid. Still, though he is expected to establish and concatenate at least the main part of the commonly accepted moral rules, he is not necessarily bound to take them as the basis on which his own system is constructed. Rather, we should expect that the history of Moral Philosophy—so far at least as those whom we may call orthodox thinkers are concerned—would be a history of attempts to enunciate, in full breadth and clearness, those primary intuitions of Reason, by the scientific application of which the common moral thought of mankind may be at once systematised and corrected.”([
This significant passage further elucidates Sidgwick’s stance towards dogmatic intuitionism. From the outset, he maintained that ‘common-sense morality is, on the whole, reasonable.’ Thus, in a certain sense, dogmatic intuitionists do indeed tell people “what they ought to think”, namely that they should accept the common-sense morality explicitly articulated by the relevant dogmatic intuitionist theory. However, dogmatic intuitionists—that is, moral philosophers—have failed to furnish supporting principles for common-sense morality, as they have never attempted to reflectively “transcend” such morality. Consequently, the crucial tasks of elucidating the history of “rational primary intuitions” and seeking “source-level” self-evident rules remain entirely beyond their reach.
Unlike moral philosophers, Sidgwick sought “truly self-evident normative principles”—that is, “principles which are both true and self-evident when considered independently of other propositions” ([
Consequently, Sidgwick proposed that any “seemingly self-evident proposition” must fully satisfy four conditions to attain “the highest degree of certainty” ([
(I) Clarity. “The terms of the proposition must be clear and precise.”
It should be noted that Sidgwick did not require the proposition itself to be clear or precise. It can be inferred that if the terms of a proposition are precise and this precision extends to the relationships embedded among the terms, then the proposition itself may also be precise. However, there is no reason to believe that “clarifying and refining terms” would make the proposition as a whole clearer. In fact, this might instead render the proposition rather ambiguous.
(II) Reflection. “The self-evidence of the proposition must be ascertained by careful reflection. ”
Intuition is neither a “pure reaction or instinct” nor a “universally held opinion”, but rather a “belief that, after prudent observation, presents itself as a ‘rational command’”. Such reflection will largely concern the origins of intuition: is it merely a product of my upbringing? Have I accepted it unthinkingly on the basis of social authority? Is it grounded in my subjective likes and dislikes? Reflection will also address “the content of the proposition itself”. Sidgwick recognised that “reflection holds particular importance in ethics”, noting that intense emotions often transform into “judgements that appear intuitive”, and that we accept many moral principles largely through reliance on external authority. Habit breeds an impulse to “observe these principles without further justification”, making it crucial to test whether the principle remains a “clear and correct intuition” after reflection.
Though Sidgwick does not explicitly state it, there is reason to believe he was also contemplating the meaning of “seemingly self-evident propositions” ([
(III) Consistency. “The propositions accepted as self-evident must be mutually consistent.”
In section 3.11, it is unclear whether Sidgwick refers to “logical consistency” or “practical consistency”. Logical consistency would exclude “two logically contradictory propositions that appear self-evident” (for example, holding that “one ought always to act spontaneously” and that “one ought always to act reflectively”). Practical consistency would not only exclude such single sets of propositions but also pairs such as “one ought always to be kind” and “one ought always to be just”. The conclusion of The Method of Ethics indicates Sidgwick was considering a “practical test”; his assertion that he found similar conflicts in numerous ethical works further confirms his focus on practical consistency when considering coherence ([
(IV) Non-dissensus.
“Since it is implied in the very notion of Truth that it is essentially the same for all minds, the denial by another of a proposition that I have affirmed has a tendency to impair my confidence in its validity ...And it will be easily seen that the absence of such disagreement must remain an indispensable negative condition of the certainty of our beliefs. For if I find any of my judgments, intuitive or inferential, in direct conflict with a judgment of some other mind, there must be error somewhere: and if I have no more reason to suspect error in the other mind than in my own, reflective comparison between the two judgments necessarily reduces me temporarily to a state of neutrality. And though the total result in my mind is not exactly suspense of judgment, but an alternation and conflict between positive affirmation by one act of thought and the neutrality that is the result of another, it is obviously something very different from scientific certitude.” ([
This argument differs from the preceding three in that it is expressed indirectly ([
While Sidgwick certainly did not intend to provoke cognitive dissonance—indeed, under a proper understanding of “conflicting principles”, the classical course of action to consider would be “suspension of judgement”—in practice, “non-dissensus” carries greater theoretical risks, revealing the inherent tension within Sidgwick’s intuitionism.
The sceptical implication of the “non-dissensus” condition is “suspension of judgement”, namely the simultaneous acceptance of “mere appearance” ([
This perceptual analogy maps directly onto the specific conflict between Rational Egoism and Utilitarianism at the heart of Sidgwick’s Dualism of the Practical Reason. Just as the two observers cannot resolve their disagreement about whether the bird is a robin or a blackbird (and thus must suspend judgement), competent moral judges cannot resolve their disagreement about whether the foundational moral principle is prudence (Rational Egoism) or reasonable benevolence (Utilitarianism). For the Rational Egoist, the self-evidence of prudence—“one ought to promote one’s own greatest good”—is as immediate as the perception of a robin; for the Utilitarian, the self-evidence of reasonable benevolence—“one ought to promote the greatest good of all”—is equally immediate, like perceiving a blackbird. Neither can demonstrate the other’s “perception” is erroneous: the Egoist does not deny the Utilitarian’s intuition of benevolence, but rejects its primacy, and vice versa. By Sidgwick’s own “non-dissensus” criterion, this irreconcilable disagreement forces both parties to suspend judgement on the self-evidence of their respective principles. This suspension of judgement is not merely a theoretical nicety—it directly undermines Sidgwick’s project of establishing a self-evident moral system, as the two foundational principles of his intuitionism (prudence and benevolence) cannot satisfy the “non-dissensus” condition. In short, the “robin/blackbird” analogy illustrates that the Dualism of the Practical Reason is not a mere practical conflict, but an epistemic failure rooted in the collapse of the “non-dissensus” criterion: just as the bird’s identity remains unresolvable, so too does the conflict between Egoism and Utilitarianism, leaving Sidgwick’s system without the certain foundation he sought.
One might argue that ‘the degree of certainty should correlate with the degree of common-sense agreement.’ Occasionally, high common-sense agreement may furnish “reasons to doubt that doubt is misplaced”. Yet ordinarily, this is not the case. Suppose 51% perceive it as a robin and 49% as a blackbird. Without delving into the intricacies of Bayesian epistemology, it follows that neither side can claim their identification possesses a “significantly higher degree of certainty”.
Moreover, Sidgwick did not fully confront the potential implications of the “non-dissensus condition”. While he did attempt in pp. 384-6 to demonstrate that “his so-called self-evident axioms coincide with the views of ‘philosophers equally capable of reflection’”, this may be interpreted as “seeking potential divergence to test his position rather than seeking agreement to support it”. Yet he fails to adequately reflect upon the fact that “reflective thinkers may also disagree with his so-called axioms”. Such disagreement is in fact inherent in his ‘The Dualism of the Practical Reason’: egoists would oppose the “principle of reasonable benevolence”, while utilitarians would challenge the “principle of prudence”.
This significant foundational divergence constitutes a crucial point Sidgwick consistently evaded in his intuitionist discourse. Although Sidgwick examined administrative means for resolving interpersonal disagreements in his political philosophy works ([
Moreover, in describing “philosophical intuitionism”, Sidgwick repeatedly employed legal analogies to emphasise that self-evident principles should possess the coercive force of law. Yet mid-19th-century British law was far from flawless, with academic debates on legal efficacy raging incessantly, debates in which Sidgwick himself was an active participant. This historical context is not merely an anecdotal aside, but a direct illustration of the failure of “non-dissensus” as a self-evident criterion. Just as mid-19th-century British law lacked intersubjective agreement (with scholars and jurists disagreeing fiercely about its foundational principles), so too did Sidgwick’s intuitionist system lack agreement on its core moral axioms. The instability of British law—its reliance on convention, precedent, and conflicting interpretations—mirrors the instability of Sidgwick’s intuitionism, which similarly lacks a universally accepted foundation due to the failure of “non-dissensus”. This parallel is not coincidental: Sidgwick’s engagement with legal debates shaped his understanding of intersubjective disagreement, yet he failed to acknowledge that the same disagreement plaguing British law also undermined his own moral system.
Thus, the internal tensions within Sidgwick’s intuitionism become fully apparent. The efficacy of “non-dissensus” as a self-evident criterion hovers between yes and no, in fact harbouring absolute objective divergence. Just as Sidgwick employed intuitionism as a method to reconcile the disagreements between egoism and utilitarianism, striving to forge a complete ethical system yet ultimately failing—“the Cosmos of Duty is thus really reduced to a Chaos”—([
Why did Sidgwick neglect to address the sceptical implications of the “non-dissensus condition”? By his own admission, its marked divergence from common sense “would render his philosophy paralysed by scepticism”. Yet in truth, had he explicitly stated that the principle of “non-dissensus” was formulated in a “self-evident” sense, and properly addressed the relationship between “as it appears to common sense” and “as it actually is”, Sidgwick could at least have elaborated further on inter subjective disagreement. Moreover, however much he evades it, “non-dissensus” does indeed open the door to universal scepticism—a consequence Sidgwick himself could scarcely escape ([
This paper has systematically examined Henry Sidgwick’s intuitionist framework as articulated in, focusing on his classification of intuition types, his four criteria for self-evidence, and the internal tension generated by the flawed “non-dissensus” criterion. The core argument of this study is that the fourth self-evidence criterion—“non-dissensus,” which requires the absence of widespread disagreement among competent judges—contains an inherent flaw that directly exacerbates Sidgwick’s famous “Dualism of the Practical Reason,” ultimately risking the reduction of his entire intuitionist system to scepticism.
To synthesise the key philosophical arguments: First, Sidgwick’s three categories of intuitionism—Perceptual, Dogmatic, and Philosophical—represent a progressive attempt to secure moral certainty, with Philosophical Intuitionism emerging as his preferred framework for identifying self-evident moral principles. However, as this paper has expanded upon, the “legal analogy” employed in Sidgwick’s discussion of Dogmatic Intuitionism reveals its fundamental limitation: legal reasoning, being conventional and positivist, cannot provide the foundational, self-evident principles Sidgwick requires for moral certainty, as it lacks the inherent epistemic authority needed to transcend context and convention.
Second, the logical mechanism connecting the failure of “non-dissensus” to the Dualism of the Practical Reason has been clarified: the epistemic failure of “non-dissensus” is the direct cause of the practical conflict in the Dualism. “Non-dissensus” demands intersubjective agreement on self-evident principles, yet the Dualism arises precisely from irreconcilable disagreement between Rational Egoism (upholding prudence) and Utilitarianism (affirming reasonable benevolence). Since neither side can be deemed “incompetent,” the failure of “non-dissensus” deprives both principles of the epistemic certainty Sidgwick seeks, creating an unresolvable practical impasse when prudence and benevolence conflict.
Third, the “robin/blackbird” perceptual analogy, which Sidgwick employs to illustrate the sceptical implications of “non-dissensus,” has been directly connected to the conflict between Rational Egoism and Utilitarianism. Just as two observers cannot resolve their disagreement about a bird’s identity (and thus must suspend judgement), competent moral judges cannot resolve their disagreement about the foundational moral principle, forcing suspension of judgement on the self-evidence of both prudence and benevolence. This suspension of judgement undermines the certainty of Sidgwick’s intuitionist system, reinforcing the link between the failure of “non-dissensus” and the Dualism of the Practical Reason.
Fourth, the historical discussion of 19th-century British law and the Liberal Party has been integrated more seamlessly into the main argument, demonstrating that these historical developments are not disconnected from Sidgwick’s epistemological analysis but are real-world manifestations of his philosophical tension. The instability of mid-19th-century British law—marked by fierce debates over its foundational principles—mirrors the instability of Sidgwick’s intuitionism, both stemming from the failure of “non-dissensus” to secure intersubjective agreement. Similarly, the Liberal Party’s 1886 schism, which Sidgwick witnessed personally, illustrates the fragmentation that results from the absence of a universally accepted foundational principle—paralleling the fragmentation of his moral system due to the Dualism of the Practical Reason.
In summary, Sidgwick’s intuitionist system is undermined by a fundamental internal tension: his pursuit of moral certainty through self-evident principles relies on the “non-dissensus” criterion, yet this criterion fails to resolve the disagreement between Rational Egoism and Utilitarianism, thereby exacerbating the Dualism of the Practical Reason. This tension, as illustrated by historical parallels with 19th-century British law and the Liberal Party, ultimately exposes Sidgwick’s system to the risk of scepticism—a risk Sidgwick himself acknowledged but failed to fully resolve. While Sidgwick’s intuitionism made invaluable contributions to classical utilitarianism and intuitionist ethics, laying the groundwork for subsequent scholarship, its internal tension remains a crucial point of analysis for understanding the limits of his project. Future research could further explore how later intuitionist philosophers (such as Moore or Ross) responded to this tension, or how contemporary epistemological theories might offer new insights into resolving the conflict between “non-dissensus” and moral dualism.