Introduction

One of the profound questions in the history of Philosophy till this date is regarding the nature and truth of knowledge. In this epistemological pursuit, Abū Ḥāmid al-Ghazālī (1058-1111), René Descartes (1596-1650) and Karl Popper (1902-1994) contributed a great deal by offering unique frameworks rooted in their historical, religious, and cultural contexts. Each one of them initiates their study with doubt; however, there ideas radically diverged when they moved forward from doubt to truth.¹.

1.1. Al-Ghazālī: From Skepticism to Mystical Certainty

Al-Ghazālī was the 11th-century Persian-Muslim scholar, theologian, jurist and mystic in the Islamic Golden Age, writing well before modern European philosophy. He lived in a deeply religious milieu and engaged with Islamic theology and philosophy (e.g., kalām, Sufism), famously documenting his journey in Deliverance from Error (c. 1100 CE).²

He began his epistemological journey with a deep crisis of doubt. In his autobiographical work Munkidh min al-Dalal (Deliverance from Error), he began to question the reliability of sense perception and reason.³ Ghazālī begins by rejecting taqlīd (blind acceptance of authority) and tests the two pillars of knowledge: sensory experience and rational intuition. Finding sensory data unreliable (illusions like the moving shadow or tiny stars prove the senses can mislead), he “resolves to rely on Pure Reason.” But then, in a thought experiment, even reason is cast into doubt by imagining a higher faculty (as reason is higher than senses).⁴ He inquired as to what is the foundation of truth if sensory experience is unreliable as it may deceive us; and reasoning can lead to conflicting conclusions (can be witnessed in Greek Philosophy)? Henceforth, al-Ghazālī not only criticized Aristotelian metaphysics in his famous work The Incoherence of the Philosophers, but also refuted rationalism and the doctrine of necessary causality.⁵ He also rejected Islamic philosophers like Avicenna who were influenced by Greek philosophy.⁶ For example, fire doesn’t necessarily cause burning: only God wills such events. Instead of causality, he gave the doctrine of occasionalism, where all cause-effect relationships are mere habits of divine will.⁷ After rejecting philosophy, he sought refuge in Islamic mysticism (Sufism). According to him, although reason is practical and have uses but it is limited. Hence, the ultimate knowledge neither comes from sensory perception nor logic or reason; rather it comes through an inner spiritual experience granted by Allah. He termed this divine illumination as kashf whose path lies in the heart that can be awakened by faith and divine will.⁸

1.2. Descartes: The Rationalist’s Quest for Certainty

René Descartes was a 17th-century French philosopher- mathematician often considered the “Father of Modern Philosophy.” Writing during the Scientific Revolution and the decline of Scholasticism, he sought a new foundation for knowledge in works like Meditations on First Philosophy (1641).⁹

Like al-Ghazālī, he went with the method of doubt. In his famous work, Meditations on First Philosophy, he recounts that he can reject all beliefs including sensory experience and mathematics.¹⁰ Descartes deliberately filters beliefs by certainty: if any belief can be doubted, he sets it aside. He begins with easy targets (sense beliefs – since sometimes senses deceive, as in optical illusions or dreams) and then escalates the doubt (e.g., “evil demon” hypothesis that absolutely everything perceived or imagined might be false). His method is hyperbolic: he exaggerates possible doubt to ensure that whatever survives this process is truly indubitable. Thence forward, ‘Cogito, ergo sum (I think, therefore I am) became his modus operandi, since he can doubt everything except the fact that he is doubting.¹¹ From this self-evident truth, Descartes rebuilds a system of knowledge based on clear and distinct ideas.¹² This procedural skepticism (outlined in Meditation I) is applied step-by-step to demolish all uncertain beliefs and find a secure foundation. He developed his epistemological thought on foundationalism as he sought to ground knowledge in absolutely certain first principles.

For Descartes, the mind is the seat of knowledge independent of the body; and through rational introspection, truth can be discovered. Consequently, he believes that reason have power to attain metaphysical truths about the external world, the self and the God.¹³ While al-Ghazālī rejected reason in favor of faith, Descartes utilized reason in order to prove and support faith.¹⁴ His famous ontological and causal arguments for the existence of God are extensively used to prove the existence of God.

1.3. Karl Popper: Knowledge without Certainty

Karl Popper (1902-1994) was an eminent and influential philosopher of science. He was an intellectual writer of modern science who has vast contribution in the fields of Philosophy of Science, Epistemology and Political Philosophy.

He took significantly a different approach from both al-Ghazālī and Descartes. He refuted the Cartesian method of Descartes on the account that for him certainty is merely an illusion. No matter a theory is plausible, it still remains probable to falsify it. Since, no theory can ever be proven true, so he rejects epistemology based on foundationalism. According to Popper, the growth of science is solely possible through a process of conjectures and refutations.¹⁵

Facts cannot prove a theory to be true, but they can show it to be false. And once shown to be false, a theory comes to represent a genuine contribution to knowledge: we can state what is not true much more definitively than we can state what is true, and consequently, refuted statements are valuable. They are not useless (as the traditional view holds); for Popper the refutation of a theory represents a real advance in scientific knowledge which should be celebrated.¹⁶

He was a strong critique of inductive reasoning.¹⁷ He proved the flaws of inductive reasoning through probability. He claimed that instead we ought to use principle of Falsifiability¹⁸ as good scientific theories risk falsification. They invite rigorous testing and may be disproved by a single counter-example. it is interesting to note that Popper neither tried to build his epistemology on a certain foundation like Descartes; nor he deemed necessary the role of Divine certainty like al-Ghazālī. To him, truths are always tentative, provisional and are subject to improvement. He is strong supporter of an open society where ideas are constantly critiqued, debated, and tested.¹⁹

Prior to Popper, epistemologists believed that knowledge is justified true belief. Although, Gettier’s critique led to number of theories that revolves around justificationism, Popper rejected justificationism as well. He defined objective knowledge as knowledge existing independently of belief, stored in books, theories, and culture; and that knowledge grows through criticism, not justification.²⁰

2. Comparative Reflection on Major Themes

The comparative Analysis of major epistemological themes in al-Ghazālī, Descartes and Popper is based on themes and aspects. the minor themes are discussed in the table below; whereas, the major themes are reflected in detail in later section.

Table 1. Comparative Analysis of minor epistemological themes in al-Ghazālī, Descartes and Popper

The following section will discuss major comparative themes:

2.1. Methodology

Al-Ghazālī started his inductive reasoning by doubting sources of knowledge one by one. Al-Ghazālī’s methodology is existential and therapeutic. He used introspective skeptical reasoning to progressively undermine certainty in all standard epistemic sources. Al-Ghazālī’s narrative is one of human impotence and the necessity of divine rescue. Al-Ghazālī explicitly denies that he can defeat skepticism through reason; only Allah can save him from solipsistic doubt. Descartes would never say he cannot defeat skepticism by human reason – indeed the whole point of his project is to do exactly that, using reason aided by God’s grace in a more implicit way.

Comparatively, in modern terms, Descartes’ skepticism is methodological and didactic.²⁶ During his quest to acquire foundational knowledge he willingly adopted Cartesian Method (Systematic methodical doubt).²⁷ But Descartes never loses confidence in reason’s ability to find truth, his narrative is one of triumphalist restoration of knowledge by one’s own cognitive power (a power he believes is God- given, yes, but it operates through natural light).²⁸

Whereas, Popper upholds that inductive reasoning is flawed. He argued that “no rule can ever guarantee that a generalization inferred from true observations, however often repeated is true”.²⁹ Hence instead of verification (as traditional theorists believed) science advances through falsification.

2.2. Source of Knowledge

For al-Ghazālī knowledge is gained by spiritual experience or Divine illumination (kashf).³⁰

The source of knowledge for Descartes is Rationalist metaphysics. In sum, he resolves doubt through self-evident reason (cogito ergo sum); and then theological verification (God as guarantor of truth).

However, for Popper Critical Rationalism and analytic philosophy are the sources of knowledge. According to him, there’s no such thing as certainty; and only tentative knowledge is possible. He embraced fallibilism—the belief that all human knowledge is inherently uncertain and provisional; and we can never possess absolute truth. Knowledge grows through error correction and critical discussion.

2.3. Role of God

The role of God is central and active cause of everything. For al-Ghazālī, God is not only the source of truth but the agent who dispels skepticism. Human efforts alone failed to overcome doubt; certitude came “from the divine liberality” as a light in the heart.³¹ Moreover, in Ghazālī’s epistemology God continuously plays a role via prophecy or inspiration – the “higher faculty” that can validate what reason cannot. In his view, God’s guidance (through prophets or mystical unveiling) is the ultimate criterion of truth, needed to ground even rational knowledge. This aligns with his theological perspective: God’s perfection ensures that what is revealed or illumined by God is real knowledge, whereas purely human faculties remain uncertain without this divine anchor.

According to Descartes, Role of God is crucial but philosophical in nature. It paves the way for absolute truth and existence. Descartes invokes God as a guarantor of knowledge’s reliability. In the Meditations, after establishing his own existence and reasoning towards God’s existence, he argues that a perfect, benevolent God would not deceive us by making our fundamental rational faculties faulty. Thus, when Descartes clearly and distinctly perceives something (e.g. that the angles of a triangle sum to 180°), God’s non- deceptive nature ensures those perceptions are true.³² God in Descartes’ system is not accessed via sudden illumination, but through rational proof; yet once proven, God plays a key epistemic role, underwriting the truth of clear and distinct ideas and dispelling the “evil demon” possibility.³³ For him, the trust in God is what ultimately allows science and reason to proceed with certainty.) It is interesting to note that Descartes’ intervention of God to validate reason; and need of reason to prove His existence led to an important critique known as ‘Cartesian circle’ (will be discussed in later sections).

Although role of god is not central to epistemological theory of Karl Popper as he claimed that “a theory that explains everything explains nothing.”³⁴ But Popper’s principle of falsifiability segregates science from pseudo-science.³⁵ According to him, if a statement or theory can be tested and potentially proven false then it is scientific. For instance, ‘All metals expand when heated’ can be falsified, hence it is scientific. On the contrary, if a statement or theory cannot be falsified, then it is metaphysical or pseudoscientific. For instance the claim that ‘God exists’ is not falsifiable so it is non-scientific.³⁶ Yet, all metaphysical claims are meaningful in other domains.³⁷

2.4. Scope and Nature of Skepticism

In Ghazālī’s thought, radical (universal) skepticism, albeit temporary, can be witnessed. Ghazālī first questioned sensory beliefs, and then even rational intuitions, allowing that “beyond the perception of reason, another judge” might exist. He entertains a scenario where all human knowledge could be illusory relative to a higher reality (e.g. the perspective of God or prophets), thus nothing in ordinary experience is immune to doubt. His skepticism is all-encompassing – senses and reason – leading to a brief but profound epistemic crisis.

Descartes skepticism is Hyperbolic in nature. He extends doubt as far as possible. He systematically doubts the evidence of senses (since they sometimes deceive) and even basic logical or mathematical truths under the hypothesis of an all-powerful deceiver.³⁸ This global skepticism (albeit methodical and provisional) means no belief – about the external world or even simple arithmetic – is initially beyond question. Descartes’ doubt is universal in scope, serving as a tool to test which beliefs can withstand the most extreme doubt. However, Popper claimed that even our best theories could be wrong.³⁹

2.5. Epistemological Implications

2.5.1. Al-Ghazālī

● Limitations of reason: al-Ghazālī concluded that sensory and rational faculties alone are insufficient for ultimate knowledge. They are conditional and dubitable.

● Faith in divine illumination: To him, true certainty comes from a supra-rational source (kashf) Thus, giving rise to an epistemology that is both fallibilist as well as mystical about ordinary knowledge.

● His approach influenced Islamic thought by emphasizing the harmony of reason and faith (faith in spiritual experience of God) ultimately completing the knowledge quest.

2.5.2. Descartes

● He laid a foundation for modern knowledge and rationalism.

● Descartes laid the foundation of Enlightenment epistemology. By identifying the thinking self as the foundation of knowledge, he shifted the philosophical focus to the subjective certainties of the mind. His insistence that knowledge must be built on indubitable beliefs led to a new standard of rational clarity in philosophy.

● His reliance on divine guarantee to secure knowledge reflects a transition within a rational system.

● Epistemologically, his methodical doubt inaugurated the modern foundationalist approach (building knowledge from self- evident truths).

2.5.3. Popper

fallibilism (scientific theories can be falsified instead of verified)

critical rationalism

Falsifiability can be use as demarcation criteria to segregate science from pseudo-science)

2.6. Influence/ Legacy

al-Ghazālī left his foot marks in Islamic theology and Sufism .

Enlightenment and modern rationalism is forever indebted to Descartes. His legacy gave rise to the Cartesian rationalism; and highlights epistemological problems that has influenced famous empiricist verse rationalist debate in later philosophical debates. Spinoza, Leibniz, Hume, and Kant are to name a few.

Popper’s epistemology has greatly influenced science, politics and education:

In science it encourages testability and openness to refutation.

It promotes critical thinking, questioning, and active engagement in education.

In Philosophy, he adopted critical rationalism; and rejected traditionally acclaimed inductivism and justificationism

He favors democratic values, freedom of speech, and open societies in political domain, while opposing totalitarian ideologies.

Culturally, Popper legacy is visualizes as a symbol of intellectual humility, openness, and rational critique

It is rather interesting to see that al-Ghazālī as a Muslim theologian culminates knowledge in spiritual union with the Divine; and Descartes envisioned his rationalism on indubitable self and supported his claims by God’s perfection. Hence, both utilized two different approaches and methods leading to similar resolutions. Contrarily, Karl Popper deconstructs both their epistemologies that lead to certainty; and instead advocates for a fallibilism of scientific ideas that can be tested but they are neither final nor certain. According to him all knowledge is provisional and certainty is impossible.

3. A Comparative Critique of Descartes, al-Ghazālī and Popper
With Respect to Their Epistemological Beliefs

Along with appreciation, each thinker invites number of criticisms. However, we will narrow down those critiques in terms of their epistemological beliefs only. Following table is description of weaknesses in their epistemological theories.

Table 2. Critique on al-Ghazālī, Descartes and Popper

4. Epistemological Relevance in Modern Era

The relevance of these eminent thinkers in modern day depends on the traditional context and the criterion as to which source of knowledge is being pursued. In al-Ghazālī we can find spiritual and fundamental-Islamic narrative; and Descartes narrative is scientific and Western. Whereas, Popper’s epistemic beliefs are purely philosophical and interdisciplinary. The following table is a comparative narrative as to who is more relevant in modern times.

Table 3. Comparative Narrative as per Relevance in the Current Era

Note: {* In this table, (---) means that the criteria is not applicable for the relevant thinker}

In closing, comparing these thinkers on the basis of their epistemologies was an interesting feat. In my opinion, in modern times Karl Popper’s view is more relevant as compares to Al-Ghazālī and Descartes. This is mainly because of two reasons:

Ever since Popper’s introduction to falsification method in philosophy of science there is no advocate of attaining certainty in Knowledge. Contemporary philosophy of science is treading by collaborating Popper’s ides with Kuhn’s paradigms, research programs of Lakatos and Bayesian epistemology in order to achieve a comprehensive understanding of knowledge.⁵⁸

In the millennium, the importance of scientific knowledge supersedes spiritual knowledge. Hence, despite the shortcomings of his theory as seen in Table 2, his revolutionary epistemological ideas remain foundational in refining the philosophy of science.

In contrast, Descartes epistemology is a precursor to modern rationalism that stimulated the empiricist-rationalist debate. However, due to his ambiguous views, he has introduced lasting tensions within epistemology. His views are of slight importance today. Similarly, al-Ghazālī attempted to synthesize reason, faith and intuition derived from philosophy, theology and mysticism. But in doing so, he created contradictions and opens his thought to critique. Although his views are still studied among Islamic mystics; but it too have little significance in current times.

Nonetheless, all three of them were popular and influential in their own times owing to their significant contributions in Islamic theology, rational metaphysics and philosophy of science respectively.