AGNOSTICISM. – It is the spiritual attitude of one who suspends judgment concerning the existence and nature of the Absolute and of the Divinity.
1) Notion. The term, introduced into circulation by Th. Huxley (1825–95), enjoyed singular success amid the proliferation of systems with a positivist and critical orientation characteristic of European philosophy from the second half of the nineteenth century until the condemnation of modernism (1907). Rather than referring to a particular system, it seeks to suggest a methodical and investigative caution that can be—and in fact has been—adopted by the most varied and even discordant systems. This caution is said to consist in suspending judgment regarding the ultimate content of things and in the consequent declaration that the human mind is incapable of attaining the problems touching upon the first origin of reality, the nature of God, and the ultimate destiny of man. In the time of St. Paul, the Athenians showed themselves agnostic: dissatisfied with the gods of the official religion, on certain particular occasions they raised altars and prayers to the unknown God (ἀγνώστῳ θεῷ: Act. 17:23). Gnostics, on the other hand, were called those heretics of the first centuries of Christianity who claimed to fathom, by the powers of pure reason, not only the content of natural religion but the revealed truths themselves. In opposition to the latter, Huxley called himself an “agnostic” and chose the term a. in order to have an “ism” with which he could present his own thought among his colleagues in the “Metaphysical Society”: by the new term he wished to warn that religious concern is, on the plane of life, no less foreign and indifferent than music and painting can be—and in fact are for many.
Agnosticism, however, must not be confused with scepticism, nor is it a “negative creed”; it is not any “creed” at all. It affirms a simple criterion of moral and scientific sobriety, insofar as it invites one to take up a position of neutrality between affirmation and negation in everything concerning the problems of the absolute. To the traditional conviction that human intelligence grasps the nature of the being of things and naturally proceeds to God, and that consideration of creatures, of the forms and modes of being of finite realities, is the “way” that permits and obliges one to recognize infinite being, Huxley opposed the new speculative situation that had arisen in modern culture through the work of Hume and Kant. Thus, according to this authoritative declaration, all philosophies that draw their direct inspiration from empirical phenomenalism and speculative criticism are to be called agnostic—that is, almost the totality of the theories of science and reason that appeared during the last two centuries, with the exceptions of Catholic philosophy and, in its own way, the totalitarian rationalism of Hegelian philosophy. Precisely because it never resolves itself into pure scepticism, every agnostic position can claim to renounce a given sector of truth because it holds firmly to the truth of another sector in which the criterion of certainty finds full satisfaction. There may therefore be multiple forms of a., according to the specific field in which one has chosen to take one’s stand.
It is scientific a. when certainty of truth is attributed to the sphere of experimental investigation; philosophical when the absolute sufficiency of speculative procedures alone is proclaimed; theological when reliance is placed solely on the communications of divine revelation. Rarely, however, is a. found realized in isolation in one of these pure forms, given the close affinity linking the three fields just mentioned.
2) Forms. – In David Hume (1711–76), one should speak not so much of a. as of confessed and radical speculative scepticism; nevertheless, his position must be recalled first because of the importance it had in the formation of Kantian thought. In Hume, the sceptical attitude toward every kind of knowledge, whether natural or revealed, follows from the logical development that he was able, with a brilliant analytic capacity, to give to the “principle of experience” posited by Locke and elaborated by Berkeley through his critique of abstract ideas and of the concept of matter. The idea of cause still remained standing, at least for spiritual substances: Hume showed that this openly contradicted the principle from which one had begun.
The starting point, in fact, is the principle that all our cognitions are distinguished, by their different degree of vividness, into “ideas” and “impressions.” The latter, which are more vivid, either derive from “unknown causes” and are called “impressions of sensation,” or are the psychic response produced by the reproduction of images within consciousness; these are called “impressions of reflection,” which are followed by ideas likewise of reflection. Only those ideas have cognitive value that can be traced back to an impression of sensation or of reflection to which they correspond exactly. If such an impression is lacking, one must conclude either that the idea in question does not exist at all, or that its origin must be sought in a special principle. It is the latter hypothesis that applies to the notion of cause and effect, upon which all knowledge of factual reality rests: experience offers only facts of mere succession, and tells us nothing about the nature of the forces that connect the succession of the phenomena of nature, or of consciousness (Treatise of Human Nature, I. I, sect. XIV). The notions of cause and effect, Hume concludes, therefore do not belong to the sphere of knowledge, but are to be considered “feelings” or persuasions generated in us by the “repetition” of experiences of succession, through which, when one of the terms (cause) appears, we are spontaneously led to expect the arrival of the other (effect). In this Hume had been preceded in antiquity by the Pyrrhonist Sextus Empiricus and, in the Middle Ages, by the Arab Algael and by a large number of scholastics of the period of decline, belonging predominantly to the nominalist school. These thinkers did not acknowledge natural reason’s capacity to prove the “preambula fidei” and explicitly doubted the necessary and universal validity of the principle of causality (Nic. of Ultricuria, P. d’Ailly, Ockham, and in part Scoto himself).
E. Kant (1724–1804), proceeding from where Hume had stopped, elaborated the new theory of knowledge.
For an intellect deprived of its own intuition, as ours is, the only kind of knowledge that makes a science possible is that of synthetic a priori judgments, in which the “matter” of phenomena is subsumed under the form of a category of the intellect. Not only the principle of causality, but all the principles of science derive their origin and value from within the subject, insofar as the subject is considered as self-consciousness. Thus the “I think” stands at the origin of every category and is therefore the transcendental condition of every valid cognition.
The only knowledge that can therefore present itself as “science” is that which results from the synthesis of a matter taken from experience and a form given a priori: pure matter is blind and without order, while pure form in itself is empty and without content. As is known, for Kant only mathematics and the new Newtonian physics result from synthetic a priori judgments and realize the form of scientific knowledge; metaphysics, on the other hand, because it claims to go beyond phenomena and grasp the noumenon, that is, the “thing in itself” of things, is left without any object and can no longer present itself as a science. When, therefore, the human intellect, bound by its nature to experience, strives to embrace the totality of being in itself and to rise to knowledge of the first Cause, asking what the world, the soul, and God are, it loses itself in inextricable “antinomies” (cf. Critique of Pure Reason, bk. II, chap. 2). The noumenon of things, the world, the soul, and God himself are indeed said to exist, but more as the limit of knowledge and the end required for its realization than as its object; only in the field of practical reason can man attain certainty concerning such objects.
More faithful to the letter of the human solution was A. Comte (1798–1857), proceeding from the principle that only what is susceptible to scientific experimentation should be accepted as true. The only truth, therefore, accessible to man is that of “facts,” catalogued on each occasion by experience, according to the manner in which they are brought to light through the filter constituted by experience itself. Knowledge is reduced to taking note of the “relations” that arise endlessly between fact and fact, in the various orders of nature; thus, for Comte no less than for Kant, to undertake the search for efficient and final causes is to try to draw water with a bottomless bucket.
Of the three epochs that Comte assigned to the development of human civilization, the religious and theological epoch was placed first and was therefore considered the most imperfect; it had vanished with the advent of philosophy, just as philosophy in turn had to yield its place to science, which is the complete and definitive form of knowledge. The French sociological school (Durkheim, Mauss, Lévy-Bruhl), applying Comte’s principles of positivism to the study of primitive peoples, explained the emergence and manifestations of natural religion as the effect of the imposition that the individual receives and undergoes purely from outside, insofar as he is a member of the clan and tribe.
H. Spencer (1820–1903) drew more directly on Kant with the “theory of the Unknowable,” placed at the beginning of the first part of the definitive exposition of his philosophy (cf. First Principles, §§ 1–34), which later forms of philosophical a. took as their inspiration.
In Comte’s scientific a., science absorbs religion, though wrongly. According to Spencer, science and religion, far from being opposed, meet precisely at the point of the ultimate determination of their respective objects. Space, time, matter, force, life, thought, freedom... for science; the creator God, one, personal, good, just, provident... for religion: in both, it is always the Unknowable that at a certain point comes forward, and it is useless to try to investigate II. Unlike W. Hamilton, however, who opened the way for him (cf. op. cit., § 24), Spencer was intent on attributing to his own a. a genuinely positive character, insofar as he proposed to take into account not only the relations of “difference,” at which Hamilton stopped, but also the “relations of resemblance.”
In this way, Spencer observes, “defined consciousness” points beyond itself to an “undefined consciousness,” and incomplete thoughts refer to complete thoughts, so that it is impossible to stop at considering the relative and conditioned without implicitly affirming the existence of the absolute and the unconditioned: atheism is therefore intrinsically unthinkable. We cannot declare that we do not know what God is without acknowledging that God exists.
Those forms of irrationalism that can be traced, more or less directly, to the mentality created by Spencer include pragmatism (W. James), intuitionism (H. Bergson), and mysticism, according to which the criterion of truth, and the very possibility of posing the problem of the absolute, are located in the actual success of action, in the subconscious impulse, and in the affective and “sympathetic” union (M. Scheler) with being and with the Absolute. Modernism (v.) also belongs to this same intellectual milieu; in its initial phase it adopted, as the encyclical Pascendi declares (Denz-U., 2072 ff.), the doctrine of a., according to which “human reason is enclosed within the field of phenomena, of things that appear, and according to the manner in which they appear, so that it has neither the right nor the capacity to go beyond their boundaries. It is therefore unable to rise to God, or to know his existence from the things that are seen; hence it necessarily follows that God in no way can be the object of science, nor can he be recognized as the subject of history.” It is then understandable why the modernists attach no importance to natural theology, the motives of credibility, or external revelation, since these are doctrines bound—as they say—to intellectualism, which in their eyes is a ridiculous system that has forever passed away. According to the encyclical, the first step to which the a. of the modernists leads is scientific and historical atheism, as its negative phase; this is followed by the positive phase that they constituted in the so-called “principle of immanence,” through which the way is opened to the interpretation of the content of natural religion and revealed dogmas. When compared with Catholic doctrine, modernism is philosophical and theological a. at the same time, although in the minds of its proponents it seeks to express the unlimited positivity and fecundity displayed by truth in the movement of the subject’s consciousness (the evolution of dogmas). At this point one may recall, as tinged with a., the tendency of certain contemporary Catholic philosophers, revealed on the occasion of the controversy concerning the analyticity of the principle of causality, according to which the truth of knowledge is not certified by a criterion of objective evidence but by an act of instinctive “trust,” by an emotional persuasion concerning reason’s capacity for truth (F. Sawicki, J. Hessen).
A new direction was taken by a. through the merit of Existentialism, founded by Soeren Kierkegaard (1813–55), but brought into vogue during the first half of the twentieth century by the German “Kierkegaard Renaissance.”
According to the theologian K. Barth, “we, as theologians, must speak of God. But we are human beings and, as such, can say nothing about God. We must know both things: our duty is (in recognizing) our inability and thereby giving glory to God.” More moderate is the a. found in the “theory of cipher” of the philosopher-physician K. Jaspers (1883). It is held that being never becomes wholly and directly present, but always by an indirect route, in the infinite forms it can assume in existence. Being, therefore, is “given” only through aspects and “particular situations,” each of which refers back to certain “fundamental situations” or “limit-situations,” the last and insurmountable of which is precisely that of “always being in a situation,” of being unable to leave one situation except on the condition of falling into another. Every particular situation of being is thus, in the eyes of the existing “individual,” nothing but a symbol and “ciphered writing” which he must interpret, proceeding solely from the content of his existence. Being, which is all-embracing totality (Das Umgreifende), can never be encompassed by the thought of the “individual”; whether it is referred to the being of reality, to that of consciousness in general, or to that of spirit, it is always given as a “limit” and never as an “object” of knowledge. The final “cipher,” to which all ciphers refer, is for Jaspers the “failure” (Scheitern) of knowledge as such, in which what has been called the “illusion of philosophy” (J. Hersch) is laid bare.
Italian actualism, with its reduction of spirit to the pure act—that is, to an act which is act without residues or laws or contents other than the actuality of the act as mediation of itself—inclines, in its later manifestations, toward a form of philosophical a. not very different from the preceding one and perhaps influenced by II. It is pan-humanism which is pan-relativism, sustained by the assertion that in philosophy one never arrives anywhere, because every solution is always a problem and every problem always a solution (Gentile).
Theological a. is generally represented by those currents of theological thought which, insisting either on the transcendence of the divinity, or on the weakness of reason as a consequence of original sin, or mistrusting reason in general, or the use of natural knowledge for interpreting the content of revealed truths, proclaim that they adhere purely to what God has made known about himself and his mysteries in Sacred Scripture and Tradition. First in chronological order are the proponents of “negative theology” (ἀποφανικὴ θεολογία) of Neoplatonic derivation, as found in the patristic age in the Pseudo-Dionysian works and in certain theologians of the early Middle Ages who accepted its thought with excessive literal fidelity. Similarly, one may recall the followers of the rigorous tradition or “Kalām” of the Muslim theologians, and the very prince of medieval Jewish theology, Rabbi Moses Maimonides, according to whom God cannot be named by created things with any positive term that does not resolve itself into a pure negation; hence calling God being, life, wisdom... has no greater propriety than calling him stone, tree, lion, and so forth. Finally, theologies that flourished in the seventeenth and eighteenth centuries were more decidedly agnostic; with the aim of opposing the excesses of libertine and Enlightenment philosophies, they denied reason even the capacity to attain any truth, including truths of the created order, and substituted the testimony of Faith and Tradition for the natural activity of reason, or resorted to a certain vision of truth in the divine essence that creates existences (v. ONTOLOGISMO). Despite the laudable intentions that may have inspired their proponents, all these theologies, no less than modernism, must be regarded as expressly condemned by the Church (cf.: Denz-U., nn. 1622-27, 1649-52, 1659-1665, 2072-80). In general, it should also be borne in mind that the critical discussion of each particular form of a., whether scientific, philosophical, or theological, entails an examination of the individual systems to which it is connected, and especially of the epistemological presuppositions that govern II.
3) Significance. - Yet the demand advanced by a. contains nothing in itself that directly conflicts with sound realism or with the most orthodox theology, such as, for example, Thomistic theology. The attitude of reserve adopted by a. with respect to the content and limits of human knowledge, both concerning connatural and finite things and with regard to the divine nature, not only can be accepted and forms an integral part of it, but belongs to the very essence of Thomistic realism and Catholic theology. However, unlike agnostic systems, which regard the negative moment of knowing as either exclusive or at least predominant, in the thought of St. Thomas it occupies a dialectical position, that is, it stands alongside and coexists with the positive moment, which it is called upon to temper and by which it is in turn tempered. Neither rationalism nor skepticism: indeed, one cannot even stop at a notion of God—or perhaps of the very reality of things—as a pure “limit,” of which one can say nothing more than that it is unknowable and ungraspable, since this would amount in practice to accepting the very skepticism rejected in words. In other terms, a. can be neither a point of departure nor a point of arrival; one may instead speak of an agnostic inspiration which serves to moderate the claims of rationalism and gives human knowledge the proper balance of knowledge ordered in itself toward truth and the Absolute, but also conditioned by the exercise of experience and by the contingencies of life. On the basis of this recognition, one could establish a gradation of the various a. mentioned above, beginning with the most extreme forms (Hume, Comte) and proceeding to the more moderate ones (Kant, Spencer), taking into account both the object to which neutrality relates and the intensity with which it is asserted.
This gradation may also be continued, though in another sense, within realist systems. A first observation is that one may well know of a thing that it in fact exists while its intimate nature remains unknown; to affirm the existence of a thing, a generic, vague, and confused knowledge of the thing is sufficient, provided that this knowledge proves to be well founded. Moreover, if of a ...
thing one has both positive and negative knowledge, positive knowledge is the first and fundamental one, for the reason that negative knowledge is called such precisely because it restricts the scope and specifies the meaning of a previous affirmative knowledge: to admit that one has of an object only negative knowledge, or that the first knowledge one has of it is negative, is to posit a state of consciousness that is impossible in fact no less than in principle. “Negative theology” is therefore necessarily preceded by “positive” or affirmative theology (καταστασία). Within positive knowledge itself, and consequently also within negative knowledge, there may then be degrees, both in virtue of what is made present in it (generic, distinct, proper...) and in virtue of the respective degree of certainty. Finally, positive knowledge, according to the differing degree of penetration into the object, may be indicative, adequate, or comprehensive. Indicative is the knowledge which, in some manner, whether a posteriori or a priori, distinct or confused, terminates in the essence of the thing; it is adequate when it distinctly grasps the essential constituents of the thing itself; it is comprehensive when it embraces all the constitutive characteristics of being, can arrange them in the ontological order that actually causes them to derive from one another, and knows how to account for all the potentialities of which they are capable in the real development of being itself.
Hence: 1) the human intellect, with the sole aid of its natural powers, can have positive knowledge that is not merely indicative, but proper and in certain cases also adequate, of the natures of the physical world, as well as of its own nature and that of the soul. Through the properties that things reveal in experience, and the soul in its operations, one can conceive the nature of the former and infer the more hidden nature of the latter. St. Thomas acknowledges that “cognoscere quid sit anima, difficilimum est” (De Veritate, X, 8 ad 8; cf. In I Sent., d. 3, 1, 2 ad 33; ibid., IV, 5; Sum. Theol., 1°, q. 87, ad 1), but he does not say that this is impossible; and the same must be admitted with regard to its properties, on which the very orientation of human life depends (spirituality and immortality). 2) The human intellect, under its natural conditions of operation, cannot attain any comprehensive knowledge either of corporeal or of spiritual substances. Such knowledge would be possible on the condition that prime matter and created freedom could be comprehended, but this is reserved to the divine intellect, which is the first Cause and first Mover and on which every contingent cause consequently depends. St. Thomas often repeats that the ultimate and constitutive differences of the essences of things are hidden from us and that we must be content to indicate them by means of their properties. 3) The human intellect, suitably disciplined, can, with the sole aid of its natural human powers, demonstrate the existence of God and recognize his principal attributes, both absolute (unity, simplicity, goodness, truth...), and relative to the created world (creator, omnipotent, omniscient, provident...). Finite things in fact manifest themselves as effects of an infinite cause, and in effects there is always manifested “in some way” a likeness of the nature of the cause. This is therefore a positive and, in a certain sense, distinct knowledge, insofar as God is clearly distinguished from every other being; nevertheless, it is a purely “indicative” knowledge, yet a real and most noble knowledge among all forms of knowledge: “Est autem, in his quae de Deo confitemur, duplex veritatis modus. Quaedam namque vera sunt de Deo quae omnem facultatem humanae rationis excedunt, ut Deum esse unum et trinum. Quaedam vero sunt ad quae etiam ratio naturalis pertingere potest, sicut est Deum esse, Deum esse unum, et alia huiusmodi; quae etiam philosophi demonstrative de Deo probaverunt, ducti naturalis lumine rationis” (C. Gent., I, 3). 4) Since the perfections found in creatures are finite in themselves, and therefore incommensurable with the infinity they possess in God, the human intellect, left to its natural resources and obliged in its operation to depend upon the senses, can never attain a proper and adequate, and still less a comprehensive, knowledge of the divine essence. In this matter we must be content with the “quia est,” without claiming to reach the “quid est,” as the Angelic Doctor explains in the continuation of the last text cited. And this same knowledge, as the holy Doctor hastens to point out in the chapter immediately following, is granted to few, is acquired with difficulty (vix) and after a long time, and not without a mixture of doubts and errors (C. Gent., I, 4; III, 39).
According to St. Thomas, “fere totius philosophiae consideratio ad Dei cognitionem ordinatur” (C. Gent., I, 4, 1; cf. In III Sent., d. 24, I, 3, sol. I). The first task is to distinguish among the perfections found in creatures those that are bound up with the materiality of sensible substances, as such—corporeity, sensation, vegetative life, and the like—which cannot in any way be attributed to God, being mixed perfections; from the pure perfections, those belonging to the pure order of being and spiritual life, such as truth, goodness, unity, beauty, intelligence, will, love, wisdom, and the like. These not only are not incompatible with God, but must be attributed to him in the highest degree, because it is only in God that they find the purity of their own formal character, whereas in creatures they possess only a deficient and participated form. The attribution of these perfections to the divine essence is therefore intrinsically dialectical, because it entails two contrary moments, which generate a movement of the intellect that here below always remains open. There is first the moment of affirmation, or the attribution to God of the pure perfections as their first and proper possessor; and there is the moment of caution, or of guarding against anthropomorphism and immediate transpositions, insofar as it is recognized that such perfections cannot exist in God in the same way in which they are found in creatures, but in another way, that is, in a manner “proportionate” to the divine essence. Predication, to put it now in technical terms, is not made according analogy (v.): it is in this moment of analogical predication that Thomistic realism satisfies the core of legitimate exigency concealed within the reservations of the a.
S. Tommaso si trova qui d'accordo con i più insigni maestri del suo pensiero. Con Aristotele, secondo il quale «Scientia de Deo non est humana possessio» (In IV Sent., d. 49, 11, 7 ad 12, citazione libera di Met., I, 2, 983 [5-10]; cf. il comm. di S. Tommaso, lect. III, n. 64). Con S. Agostino: «Sicut dicit Augustinus: Deus formam omnem intellectus nostri subterfugit» (In IV Sent., d. 49, 11, 1 ad 3, cit. vaga di Epist. 147 [De videndo Deo ecc.] 6-8: PL 33, 596 sgg.). Con il misterioso autore del libro De causis per il quale: «Causa prima superior est omni narratione» (prop. v; ed. O. Bardenhewer, pp. 69-71). E soprattutto con lo Pseudo Dionigi Areopagita, che S. Tommaso, insieme con tutti i suoi contemporanei, ritenne per discepolo dell'Apostolo e che in questa materia dei «Nomi Divini» scelse a suo principale maestro. Ed ecco i principi della dottrina di questo profondo teologo, ricordati da S. Tommaso un po' dappertutto nelle sue opere e radunati nel commento alla citata proposizione del De causis (lect. VI). Con il vivo senso della divina trascendenza, che aveva attinto dal neoplatonismo, lo Pseudo Dionigi afferma che parlando di Dio «sono più vere le negazioni, che le affermazioni» (Coel. Hierarchia, cap. 2: PG 3, 141 A). La ragione di ciò è da vedere nel fatto che Dio non si fa presente in modo adeguato a nessuna delle nostre facoltà: «né al senso né alla fantasia, né all'opinione, né al discorso, né alla scienza»; «Dio è insieme ἀνώνυμος e πυλώνυμος» (Div. Nom., cap. 6: PG 3, 587 B; 595 D). Più esplicitamente, nella versione citata da S. Tommaso:
« Si cognitiones omnes existentium sunt, et si existentia finem habent, in quantum scilicet finite participant esse; qui est supra omnem substantiam, ab omni cognitiones est segregatus » (Dio. Nom., cap. 6: PG 3, 594 A; cf. 587 D) Così che non ci si può sorprendere, quando Dionigi afferma che l'uomo in questa vita « unitur Deo sicut omnino ignoto » (Myst. Theol., cap. 1: PG 3, 1101 A). Inutile l'osservare che l'An-
gelico nel suo commento al De Divinis Nominibus, come in tutte le sue opere, si mantiene fedele allo spirito di questa dottrina, dandole una veste più rigorosa e scientifica: « Hoc est ultimum ad quod pertingere possumus circa cognitionem divinam in hac vita, quod Deus est supra omne id quod a nobis cogitari potest et ideo nominatio Dei quae est per remotionem, est maxime propria » (cap. 1, 1, 3, ed. Parm., t. XV, 271 b). E nel Prologo a Sum. Theol. 1ª, q. 3: « Cognito de aliquo an sit, inquirendum restat quomodo sit, ut sciatur de eo quid sit. Sed quia de Deo scire non possumus quid sit, sed quid non sit: non possumus considerare de Deo quomodo sit, sed potius quomodo non sit » (cf. In I Sent., d. 2, 1, 3, ad 2; C. Gent., III, 39; 49 e passim).
ANALOGIA (v.) fa capo nel tomismo ai principi indicati i quali offrono la chiave per decifrare in senso positivo il mistero dell'umana esistenza e per avvicinarsi all'incommensurabile abisso della divina trascendenza.
philosophie de St. Thomas, Parigi 1918, p. 72 sgg.; E. R. Dodds, The Elements of Theology of Proclus, Oxford 1932 (v. pp. 310-313, Appendice 1: The Unknown God in Neoplatonism, ove si riassume con importanti rilievi critici l'opera di E. Norden, Ἀγνωστος Θεός, Lipsia 1913). - I teologi moderni trattano dell'a, di solito nell'apologetica (cf. R. Garrigou-Lagrange, De revelatione, I, 3ª ed., Roma 1929, pp. 276-318), oppure nella parte introduttoria al trattato dogmatico « De Deo Uno » (cf. Fr. Diekamp, Theol. Dogm. Manuale, I, ed. lat., Tournai - Parigi 1933, pp. 126-31). - Intorno allo spencerismo: G. J. Lucas, Agnosticism and Religion, being an Examination of Spencer's Religion of Agnosticism, Londra 1895. - Esposizione e critica dei sistemi: G. Michelet, Dieu et l'Agnosticisme contemporain, 3ª ed., Parigi 1909; A. Zacchi, Filosofia della religione, parte I: Dio, I: « La negazione », 2ª ed., Roma 1925, p. 167 sgg.; R. Garrigou-Lagrange, Dieu, son existence et sa nature: solution thomiste des antinomies agnostiques, 5ª ed., Parigi 1928, (fondamentale). - Fra gli articoli d'insieme: M. Chossat, s. V. in DFC, I, coll. 1-76; trattazione pressoché completa, ricca di materiali e di acuti raffronti, ma farraginosa e non scevra di una certa soggettività nell'impostazione dei problemi.