Xenophanes: 'If Horses Had Gods, They Would Look Like Horses' — The First Philosopher to Question Religious Critique and the Limits of Knowledge

Conclusion First (Key Takeaways)

• Critique of Anthropomorphism: Xenophanes criticized the Homeric and Hesiodic gods as "projections of human form," exposing the cultural and psychological origins of religious belief. This is the starting point of Western religious critique and the study of religion.
• Awareness of the Limits of Knowledge: He declared that "certain truth is unattainable by humans" (Fragment B34), making the earliest statement of fallibilism. At the same time, he stated that "through seeking, in time, humans discover what is better" (Fragment B18), expressing confidence in the gradual progress of knowledge. The coexistence of doubt and inquiry — this is the very spirit of modern science.
• Philosophical Monotheism: He proposed "one god, greatest among gods and humans" (Fragment B23), envisioning a transcendent being that thinks and governs the world in a manner entirely unlike humans. He developed a unique theology standing between Greek polytheism and a monotheistic intuition.
• Social Critique: He criticized the excessive glorification of Olympic victors and argued that wisdom (sophia) is truly beneficial to the city-state. He was the first philosopher to address "the social role of the intellectual."

Life and Historical Context

Xenophanes was born around 570 BCE in the Ionian city of Colophon (Κολοφών) (Diogenes Laërtius, Lives IX.18). Colophon lay about 60 km northwest of Miletus and was known in the ancient world for its dyeing industry and cavalry. However, as Xenophanes himself testifies in Fragment B3, the citizens of Colophon had learned "useless luxury (habrosyne / ἁβροσύνη)" from the Lydians, draping themselves in purple garments and anointing their hair with perfumed oil — a picture of decadence.

In 546/545 BCE, when Cyrus the Great of Persia destroyed Lydia and conquered all of Ionia, Xenophanes was 25 years old. He left his homeland and spent the next 67 years wandering the Greek world (Fragment B8). He is reported to have been active in Zancle (modern Messina) and Catana (modern Catania) in Sicily, and to have sojourned near Elea in southern Italy. There is no doubt that this wandering life furnished him with a comparative perspective on different cultures and religious views. That Ethiopian gods have dark skin and Thracian gods have blue eyes and red hair — this observation (Fragment B16) is the insight of a wandering poet who had come into contact with diverse peoples.

Unlike the Milesian natural philosophers, Xenophanes philosophized not in prose but in verse (poetry). He composed his works in elegiac couplets and hexameters and is said to have recited them himself at symposia (drinking parties) and public gatherings. In other words, he was a "speaking philosopher" before he was a "writing philosopher," and at the symposium — the Greek venue of education and culture — he criticized Homer and Hesiod before a live audience. This required intellectual courage, for Homer's poems held a cultural authority for the Greeks comparable to that of the Bible.

Ancient tradition (Plato, Sophist 242d; Aristotle, Metaphysics 986b21) identifies Xenophanes as the founder of the Eleatic school and as a teacher of Parmenides. Most modern scholars, however, are skeptical of this attribution. Xenophanes's claim that "all things are one" (as attributed by Aristotle) and Parmenides's argument that "Being is one" differ significantly in method and scope. It is more appropriate to understand Xenophanes as an independent thinker unaffiliated with any particular school — a wandering critical intelligence.

Among Xenophanes's literary genres, the Silloi (Σίλλοι / satirical poems) are of particular importance. These were poems offering satirical criticism of other poets and philosophers — a form so well known in antiquity that the Pyrrhonist philosopher Timon of Phlius (3rd century BCE) later composed a work of the same name in imitation of Xenophanes. Xenophanes was not merely a theorist but also a performer who enacted his critique of intellectual authority in public.

According to Fragment B8 (Diogenes Laërtius, Lives IX.19), Xenophanes was still reciting poetry at the age of 92 and beyond. He is thought to have died around 478 BCE, though the exact year of his death is unknown.

Mini Timeline

• c. 570 BCE: Born in Colophon, Ionia
• 546/545 BCE: Persian conquest of Ionia. Leaves Colophon at age 25, beginning a life of wandering
• 540s–530s BCE: Active in Sicily (Zancle, Catana). Recites philosophical poetry at symposia
• 530s–510s BCE: Active in southern Italy (Magna Graecia). Possibly sojourns near Elea
• 500s BCE: Still composing poetry at the age of 92 and beyond (Fragment B8)
• c. 478 BCE: Dies (estimated). 67 years of wandering

What Did Xenophanes Ask?

Xenophanes's adversary was not "the principle of nature," as it was for Thales and Anaximander, but the very foundation of Greek culture itself. Homer's Iliad and Odyssey, Hesiod's Theogony and Works and Days — these were not mere literary works for the Greeks but the basis of education, the standard of morality, and the "official view" of the gods. Greek boys grew up reciting Homer by heart and formed their worldview through the stories of Homer's gods.

Xenophanes confronted this cultural authority head-on. In Fragment B11 he states:

"Homer and Hesiod have attributed to the gods all the things that among humans are a shame and a reproach — theft, adultery, and mutual deception." — Xenophanes, Fragment B11 (Sextus Empiricus, Against the Mathematicians IX.193)

The problem is not merely that the stories of the gods are "immoral." The more fundamental question is: Why do humans create gods that resemble themselves? And are such gods "true"?

In other words, Xenophanes's inquiry has a double structure. First, a critique of religious representation — is what humans say about the gods merely a projection of themselves? Second, the limits of knowledge — can "truth" about the gods (or about anything at all) ever be known? The former is a question for the study of religion and religious critique; the latter is a question for epistemology. Xenophanes was the first philosopher to raise both questions simultaneously.

Crucially, these two questions are logically interconnected. If, whenever humans speak about the gods, they inevitably project their own image — that is, if human cognition is constrained by cultural and bodily conditions — then humans cannot reach "truth itself" beyond the limits of their own cognition. The critique of anthropomorphism provides the concrete grounds for epistemological skepticism, while epistemological skepticism universalizes the philosophical scope of the anthropomorphism critique. The two are not separate claims; they are two sides of the same insight.

Core Theories

1. Critique of Anthropomorphism — The Gods Are a Mirror of Humanity

Xenophanes's critique of anthropomorphism has a three-stage logical structure. The first stage (B11) is a moral critique — Homer's gods are immoral. The second stage (B14) is a structural critique — humans fashion gods in their own image. The third stage (B15–B16) is a cross-cultural proof — different peoples have gods of different appearances, and if animals had religion, they would create gods resembling themselves. Let us examine each stage in turn.

The first stage is the already-cited B11 (Homer and Hesiod attributed immoral acts to the gods). The following Fragment B14 bridges the moral critique to the structural critique:

"But mortals suppose that the gods are born, wear their own clothes, have voices and bodily forms like their own." — Xenophanes, Fragment B14 (Clement of Alexandria, Stromateis V.109.2)

Here Xenophanes points out that the problem is not confined to Homer's individual depictions but lies in a universal human cognitive tendency — imagining the gods on the model of oneself. As the decisive evidence for this structural critique, the most famous fragments, B15 and B16, follow:

"If cattle and horses and lions had hands, or could draw with their hands and create works of art like those made by humans, horses would draw the forms of the gods like horses, and cattle like cattle, each making the gods' bodies in the image of their own." — Xenophanes, Fragment B15 (Clement of Alexandria, Stromateis V.109.3)

"Ethiopians say that their gods are snub-nosed and dark-skinned; Thracians, that theirs have blue eyes and red hair." — Xenophanes, Fragment B16 (Clement of Alexandria, Stromateis VII.22.1)

The structure of this argument is clear. (1) Different peoples believe in gods of different appearances. (2) Each people's gods resemble that people's own appearance. (3) If animals had religion, they too would create gods resembling themselves. (Conclusion) Therefore, the "appearance" of the gods is a projection of the believers' own form, not an attribute of the gods themselves.

This argument was revolutionary on two counts.

First, the germ of cultural relativism. The perspective that religious beliefs are not "absolute truths" but products formed from the standpoint of a particular culture or people predates Herodotus's comparative cultural study (Histories III.38, the anecdote of Cambyses) and is a distant precursor to modern sociology of religion (Durkheim, Weber) and anthropology of religion (Evans-Pritchard).

Second, the prototype of projection theory. God is the externalization of the human self-image — this insight is structurally identical to the "projection theory (Projektionstheorie)" systematized by Feuerbach in The Essence of Christianity in the 19th century, and directly connected to Freud's account of religion (The Future of an Illusion, 1927). That the same structure of critique was repeated across a span of 2,400 years testifies to the radical nature of this question.

It should be noted, however, that what Xenophanes performed was not a denial of the "existence" of the gods but a critique of their "representation." He did not say "the gods do not exist." He said "What humans say about the gods is merely a projection of themselves." This distinction is of decisive importance.

2. Philosophical Monotheism — "One God, Greatest among Gods and Humans"

Critique alone does not make philosophy. Having rejected gods fashioned in the human image, Xenophanes went on to present a positive concept of the divine. Fragments B23–B26 articulate this:

"One god, greatest among gods and humans, in no way similar to mortals either in body or in thought." — Xenophanes, Fragment B23 (Clement of Alexandria, Stromateis V.109.1)

This god sees as a whole, thinks as a whole, and hears as a whole (B24). By the power of thought alone, without effort, it shakes all things (B25). It always remains in the same place, not moving at all (B26). In striking contrast to Homer's gods, who run, rage, feel jealousy, and commit adultery like humans, Xenophanes's god is non-human, non-material, and non-kinetic.

A point of scholarly debate is whether this constitutes strict monotheism or rather henotheism — acknowledging one supreme god without denying the existence of other gods. The phrase in B23 "among gods and humans (ἔν τε θεοῖσι καὶ ἀνθρώποισι)" can be read as presupposing the existence of multiple "gods." Lesher (1992) emphasizes this point and argues that Xenophanes's position is closer to "monarchical theology" than strict monotheism.

Barnes (1979), on the other hand, dismisses the expression as a conventional epic formula and interprets it as substantially monotheistic.

Whichever interpretation one adopts, Xenophanes's god is structurally similar to Parmenides's later "Being (to eon)" — immovable, unchanging, and one — and serves as one starting point of a grand intellectual lineage flowing through Plato's theory of Forms, Aristotle's "Unmoved Mover," and into the concept of the one God in Christian theology and Islamic philosophy.

3. The Limits of Knowledge — "Certain Truth Is Known to No One"

Xenophanes's philosophically deepest insight is condensed in Fragment B34:

"And as for certain truth (τὸ σαφές / to saphes), no man has known it, nor will there be anyone who knows it, about the gods and about all things of which I speak. For even if someone should chance to say what has come to pass, he himself does not know it. But seeming (δόκος / dokos) is allotted to all." — Xenophanes, Fragment B34 (Sextus Empiricus, Against the Mathematicians VII.49; Plutarch, Table Talk IX, 746B)

This fragment is one of the most important declarations in the history of Western epistemology. Three points deserve attention.

First, unrestricted universality of scope. He says not merely "about the gods" but "about all things of which I speak." The limits of knowledge extend not only to religious knowledge but to all knowledge. Natural philosophy, politics, ethics — everything humans say is merely "dokos (seeming, opinion)."

Second, the problem of contingency. "Even if someone should chance to say what has come to pass, he himself does not know it" — this is the earliest formulation of the problem of epistemic justification. Uttering a true proposition and knowing that it is true are two different things — this insight is a direct precursor to Plato's definition in the Theaetetus of knowledge as "justified true belief" and extends to the contemporary Gettier problem (1963) — that justified true belief is not a sufficient condition for knowledge.

Third, coexistence with the positive affirmation of inquiry. In Fragment B18, Xenophanes states:

"The gods did not reveal all things to mortals from the beginning. But by seeking, in time, humans discover what is better." — Xenophanes, Fragment B18 (Stobaeus, Anthology I.8.2)

Read together, B34 and B18 reveal that Xenophanes's epistemological position is none other than fallibilism: "Absolute truth is impossible, but gradual improvement is possible." This is structurally identical to the spirit of modern science — theories are provisional and open to refutation, but through inquiry they can progress toward better theories — and can even be called an anticipation, by 2,500 years, of Karl Popper's philosophy of science (Conjectures and Refutations, 1963). Popper himself praised Xenophanes highly as the "founder of critical rationalism" (Popper, "Back to the Presocratics," lecture 1958, published 1963).

Fragment B35 is also noteworthy:

"Let these things be accepted as resembling the truth (ἐοικότα τοῖς ἐτύμοισι)." — Xenophanes, Fragment B35 (Plutarch, Table Talk IX, 746B)

This shows that Xenophanes applied the epistemology of B34 to his own natural-philosophical claims as well. "Earth and water are the fundamental principles," "The celestial bodies are burning clouds" — even these claims of his own, he acknowledges, are not "certain truth" but merely "things resembling the truth." This self-referential intellectual humility — refusing to absolutize one's own theories — is an exceedingly rare attitude in the history of philosophy, directly connected in spirit to Socrates's "knowledge of one's own ignorance" and Popper's "falsifiability."

4. Natural Philosophy — Earth and Water, Fossils and Clouds

While Xenophanes's fame rests on his religious critique and epistemology, he also attempted rational explanations of natural phenomena, much like the contemporary Milesian natural philosophers.

According to Fragment B29, "All things come from earth, and to earth all things return." Fragment B33 states that "We are all born of earth and water." According to the testimony of Hippolytus (Refutation of All Heresies I.14), Xenophanes posited earth and water as the two fundamental principles of all things. This is dualistic compared to Thales's "water" or Anaximenes's "air," occupying a transitional position toward Empedocles's later four-element theory.

Of particular note is Xenophanes's attention to fossils. According to the same testimony from Hippolytus, Xenophanes discovered shell fossils in the quarries of Syracuse, leaf fossils of laurel on Paros, and marine-organism fossils on Malta, and inferred on this basis that the earth was once covered by the sea. He then envisioned a cyclical earth history in which the earth sinks once more into mud, humanity perishes, and when the mud eventually dries, humanity is born again. Reading fossils as "evidence of a former sea" — this method of inference is one of the earliest examples of geological thinking.

Xenophanes also attempted rational explanations of meteorological phenomena. According to Aëtius's testimony, the sun, moon, and stars are all "burning clouds" — moisture evaporated from the sea that accumulates in the upper atmosphere and ignites. The sun arises anew each day (testimony for Fragments B31–32), and the rainbow is merely a "colored cloud" (Fragment B32). The luminous phenomenon on ships known as "St. Elmo's fire" was also explained as the glow of small clouds. The attempt to explain everything through the unified process of "evaporation of water → cloud formation → ignition" aligns with the Milesian school's aspiration toward monistic explanation.

5. Social Critique — Wisdom Is More Valuable Than Athletic Victory

Xenophanes's critical spirit extended beyond religion and nature to the values of Greek society itself. The longest surviving fragment, Fragment B1, describes the kind of symposium Xenophanes envisioned. The floor is swept clean, the cups are washed, and garlands and perfumed oil are prepared. But the crucial point is what should be spoken at such a symposium — not mythological fictions of "the battles of Titans, Giants, and Centaurs" but "reverence for the gods and righteous conduct." In other words, Xenophanes sought to transform the cultural space of the symposium itself from Homeric entertainment into a venue for intellectual and ethical inquiry.

Fragment B2, moreover, is the earliest "social position statement" by an intellectual in ancient Greece:

"Even if one should win a victory at Olympia in the foot-race, the pentathlon, or wrestling — for all that, the city-state would not be better governed. A city's treasury is enriched when its citizens possess good wisdom (σοφίη / sophiē)." — Xenophanes, Fragment B2 (Athenaeus, Deipnosophistae X, 413F–414C)

In ancient Greece, victors at the Olympic Games were celebrated as heroes and granted lifelong privileges by their home city-states (meals at public expense, front-row seats, and more). Xenophanes directly challenged this culture, arguing that intellectual excellence (sophia) is more beneficial to the city-state than physical prowess.

This claim is a precursor to Plato's "philosopher-king" idea (Republic, Books V–VII), and at the same time the earliest expression of the question "What responsibility do intellectuals bear toward society?" — a question that extends to contemporary debates on public intellectuals and STEM education.

Key Works Guide

Xenophanes wrote in verse, and approximately 40 fragments survive (DK 21 B1–B45). The following is a guide to the literature for reconstructing his thought.

• Introductory: Diogenes Laërtius, Lives of the Eminent Philosophers, IX.18–20 — A concise biographical overview of Xenophanes's life and achievements. The starting point for understanding the ancient view of his relationship to the Eleatic school.
• Introductory: Patricia Curd & Daniel W. Graham, eds., The Oxford Handbook of Presocratic Philosophy, Oxford UP, 2008 — Surveys the latest research on early Greek philosophy, including multiple essays on Xenophanes's epistemology and theology.
• Intermediate: G. S. Kirk, J. E. Raven, M. Schofield, The Presocratic Philosophers, 2nd ed., Cambridge UP, 1983, Ch. 5 — A critical examination of all of Xenophanes's fragments and testimonies. Provides the most detailed discussion of the epistemological interpretation of B34.
• Advanced: J. H. Lesher, Xenophanes of Colophon: Fragments, University of Toronto Press, 1992 — A major monograph on Xenophanes. Contains English translations, commentary, and philosophical analysis of all fragments, including detailed treatment of the monotheism vs. henotheism debate.
• Advanced: K. Popper, "Back to the Presocratics" (lecture 1958, published in Conjectures and Refutations, 1963) — A landmark essay in which Popper reassesses Xenophanes's epistemology within the context of modern philosophy of science.

Major Criticisms and Debates

1. Heraclitus's Ridicule (Contemporary): Heraclitus of Ephesus singled out Xenophanes by name as a representative of "much learning (polymathiē)" (Fragment B40). For Heraclitus, the accumulation of broad knowledge was not true wisdom (sophia): "Much learning does not teach understanding (nous)." The contrast between Xenophanes's wide-ranging, encyclopedic approach and Heraclitus's concentrated focus on a single, deep Logos presents an interesting tension between "breadth of knowledge" and "depth of knowledge."

2. Aristotle's Cool Assessment (Later): In Metaphysics I.5 (986b21–27), Aristotle mentions Xenophanes, noting that he "looked to the whole heavens and said that the One is god," but then judged that he "made nothing clear (οὐθὲν διεσαφήνισεν)" and "seems not to have grasped the nature of either of these [the material or the formal]." Whereas Parmenides arrived at "the One according to reason (logos)," Xenophanes's "One" was, in Aristotle's view, logically unclear. This assessment reflects Aristotle's tendency to undervalue Xenophanes's poetic and rhetorical style of philosophy from the standpoint of logical rigor.

However, if one holds that philosophy should encompass not only logical rigor but also cultural critique, social commentary, and epistemological humility, then Aristotle's evaluative criteria themselves are called into question.

3. The "Founder of the Eleatic School" Question (Ancient to Modern): Plato (Sophist 242d) speaks of "the Eleatic tribe, beginning from Xenophanes," positioning him as a precursor of Parmenides. Most modern scholars, however (Lesher 1992, Kirk & Raven 1983), question this attribution. Xenophanes's "one god" is a theological claim, while Parmenides's "Being is one" is an ontological and logical argument. Because their methods, contexts, and argumentative structures differ significantly, placing both within the same intellectual lineage requires caution.

4. The Interpretation of B34 (Modern): Is Fragment B34 a declaration of "skepticism" or of "fallibilism"? The ancient skeptic Sextus Empiricus cited Xenophanes as a precursor of his own school, but when read together with Fragment B18 ("through seeking, humans discover what is better"), Xenophanes's position is not the skepticism that denies the possibility of knowledge altogether but rather a fallibilism that acknowledges the provisionality of knowledge while affirming the value of inquiry. This interpretation is now the prevailing one (Fränkel 1925, Popper 1963, Lesher 1992).

Influence and Legacy

Antecedent Thought: Milesian natural philosophy (the framework of rational world-explanation), the epic tradition of Homer and Hesiod (as the target of critique), comparative cultural knowledge of the eastern Mediterranean (acquired through a life of wandering). Xenophanes extended the rationalism of the Milesian school from "nature" to "religion, culture, and knowledge."

Parmenides and the Eleatic School: Xenophanes's "one god" — immovable, governing all things through thought — is structurally similar to Parmenides's "one Being (to eon)" — ungenerated, imperishable, unchanging, immovable. Even if a direct teacher–student relationship is doubtful, it is highly likely that Xenophanes's theology provided some stimulus to Parmenides's ontology.

Socrates and the Elenctic Method: Xenophanes's attitude of "questioning common sense and criticizing authority" resonates deeply with Socrates's elenctic method — examining the received opinions of interlocutors and bringing them to an awareness of their own ignorance. Socrates's "knowledge of ignorance" and Xenophanes's B34 ("certain knowledge belongs to no one") stand on the same ground of intellectual humility.

Ancient Skepticism: Sextus Empiricus (2nd century CE) regarded Xenophanes as an important precursor of skepticism and discussed him at length in Outlines of Pyrrhonism. While the attribution has been criticized as over-reading, it is certain that B34 served as a significant source of inspiration for later skeptical thought.

Modern Religious Critique: Xenophanes's critique of anthropomorphism flowed into three major modern intellectual traditions. (1) Feuerbach's projection theory (1841) — the religious philosophy holding that God is the externalization of human nature. (2) Freud's psychology of religion (1927) — the psychoanalytic view that God is a cosmic projection of the father figure. (3) Durkheim's sociology of religion (1912) — the social-scientific analysis that religion is an expression of social solidarity. All three represent the refinement, using their respective methodologies, of Xenophanes's fundamental insight: "When humans speak about God, they are really speaking about themselves."

Philosophy of Science: Karl Popper assessed Xenophanes's B34 and B18 taken together as the earliest precursor of "critical rationalism." "Certain truth cannot be reached, but through criticism and examination, we can asymptotically approach better theories" — the core thesis of Popper's philosophy of science is structurally identical to Xenophanes's insight of 2,500 years earlier.

Connection to the Present

Xenophanes's legacy lives on in the present with striking multidimensionality.

First, "awareness of cognitive bias." Humans tend to feel that what resembles themselves is "correct" or "natural." Xenophanes's critique of anthropomorphism was the earliest identification of the cognitive distortions that modern cognitive psychology precisely describes as "confirmation bias," "in-group bias," and "naïve realism." In the age of social media, filter bubbles and echo chambers — phenomena in which only opinions resembling one's own are echoed back, coming to appear as "the truth of the world" — are nothing other than the digital version of the structure of anthropomorphism that Xenophanes identified.

"Is the world you see merely a projection of yourself?" — this question remains as sharp today as it was 2,500 years ago.

Second, "fallibilism as intellectual humility." The history of medicine provides a vivid example. Physicians once performed surgery without washing their hands and attempted to cure disease by bloodletting. They were convinced of their correctness — precisely the condition described by B34: "Even if someone should chance to say the truth, he himself does not know it." Science advanced because it institutionalized the attitude of always remaining aware of the possibility of one's own error — fallibilism. Peer review, replication, falsification experiments — the mechanisms of modern science are the institutional realization of the intellectual humility that Xenophanes demonstrated 2,500 years ago.

Third, "critical examination of authority." Just as Xenophanes criticized Homer — the absolute authority of his day — modern critical thinking education places at its heart the attitude of "not blindly following the authority of sources." Fake news, deepfakes, authoritarian information control — "It is correct because many people believe it," "It is correct because an authority said it" — the danger of such reasoning was first demonstrated philosophically by Xenophanes.

Questions for the Reader

• Among the values and beliefs you feel are "obvious," "natural," or "correct," are there any that are actually nothing more than projections of your own culture, position, or experience? Try looking at them again through Xenophanes's eyes.
• "Certain truth cannot be known" (B34) and "Through seeking, humans discover what is better" (B18) — Do these two claims contradict each other, or can they coexist? How do you reconcile them in your own work or studies?
• Xenophanes argued that the wise should be honored above Olympic athletes. In modern society, too, the compensation of athletes and entertainers far exceeds that of scientists and educators. Is this disparity justified? How would Xenophanes argue?
• Xenophanes declared that "certain truth cannot be known" and yet applied that very principle to his own doctrines (B35). Can we maintain the same humility toward our own beliefs and convictions?

References

• Primary Source (Fragments and Testimonies): H. Diels & W. Kranz, eds., Die Fragmente der Vorsokratiker, Vol. 1, chapter on Xenophanes (DK 21). Contains Fragments B1–B45 and all testimonies (A section).
• Primary Source (New Edition of Fragments): A. Laks & G. W. Most, eds., Early Greek Philosophy (Loeb Classical Library 524–532, Harvard UP, 2016) — A new standard edition replacing DK. Contains all fragments and testimonies with facing Greek text and English translation.
• Primary Source (Testimonies): Aristotle, Metaphysics I.5 (986b18–27); Plato, Sophist 242d; Sextus Empiricus, Against the Mathematicians VII.49, IX.193.
• Primary Source (Biography): Diogenes Laërtius, Lives of the Eminent Philosophers, IX.18–20.
• Secondary Source (Major Study): J. H. Lesher, Xenophanes of Colophon: Fragments, University of Toronto Press, 1992 — A major monograph on Xenophanes, with annotated examination of all fragments. It offers detailed analysis of the monotheism/henotheism debate and the epistemological interpretation of B34.
• Secondary Source (Standard Reference): G. S. Kirk, J. E. Raven, M. Schofield, The Presocratic Philosophers, 2nd ed., Cambridge UP, 1983, Ch. 5 — The standard reference for rigorous examination of Xenophanes's fragments and testimonies.
• Secondary Source (Philosophy of Science): K. Popper, "Back to the Presocratics" (lecture 1958, published in Conjectures and Refutations, 1963) — A landmark essay reassessing Xenophanes as a precursor of critical rationalism.
• Secondary Source (Pioneering Epistemological Study): H. Fränkel, "Xenophanesstudien" (1925; later revised and incorporated into Dichtung und Philosophie des frühen Griechentums, 1962) — A landmark essay offering the first precise analysis of the epistemological interpretation of B34. The starting point of modern Xenophanes scholarship.
• Secondary Source (Handbook): P. Curd & D. W. Graham, eds., The Oxford Handbook of Presocratic Philosophy, Oxford UP, 2008 — Surveys the latest research trends in early Greek philosophy, including multiple essays on Xenophanes's epistemology and theology.