Schools of Indian Philosophy

Introduction to the Indian Philosophical Landscape

The intellectual history of the Indian subcontinent is characterized by a rigorous, deeply analytical, and systematic exploration of human existence, the nature of reality, and the ultimate purpose of life. Philosophy in ancient India was not merely an academic exercise; it was termed Darshana, a Sanskrit word translating to "vision" or "the way of seeing". It arose from a profound existential inquiry into the mysteries of life, the ubiquity of suffering, and the pursuit of ultimate liberation (Moksha, Nirvana, or Kaivalya). Over millennia, this relentless intellectual exploration crystallized into highly sophisticated and distinct schools of thought, each offering comprehensive metaphysical, epistemological, and ethical frameworks.

Historically, the diverse landscape of Indian philosophical systems is broadly classified into two grand traditions based on a singular epistemological criterion: their acceptance or rejection of the supreme authority of the ancient Vedas. The Orthodox (Astika) schools acknowledge the Vedas as an infallible source of knowledge. It is crucial to note that in the context of Indian philosophy, Astika does not necessarily denote theism (belief in a creator God), but rather an allegiance to Vedic revelatory authority. Conversely, the Heterodox (Nastika or Sramana) schools emerged as a radical rebellion against Vedic ritualism, rejecting the authority of the texts, the dominance of the Brahminical clericalism, and the rigid socio-religious hierarchies of the period.

The emergence of these diverse schools did not happen in isolation. The 6th century BCE was a period of massive socio-economic transformation in the middle Gangetic plains. The transition to an iron-based agricultural economy generated massive surplus wealth, leading to rapid urbanization and the rise of a powerful merchant class (Vaishyas). Simultaneously, the warrior class (Kshatriyas) began asserting intellectual and political dominance against the ritual monopoly of the Brahmanas. This dynamic socio-economic background fostered the Sramana (wandering ascetic) movement, which served as the crucible for heterodox thought.

This exhaustive report dissects both the Orthodox and Heterodox schools, detailing their core philosophies, epistemological frameworks, ontological classifications, theories of causation, and theories of perceptual error. It provides a robust analytical foundation tailored for advanced civil services preparation, weaving historical context with philosophical nuance to address both Preliminary and Mains examination paradigms.

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Part I: The Six Orthodox Schools (Shad Darshana)

The six orthodox systems (Shad Darshana) were formally codified during the ancient and medieval periods of Brahmanic-Sanskritic scholasticism, though their conceptual roots trace back to the early Vedic and Upanishadic eras. They evolved concurrently, engaging in centuries of fierce intellectual debate, which only served to sharpen their respective logical frameworks. Conceptually, they are grouped into three logical pairs based on complementary metaphysical and practical methodologies: Samkhya-Yoga, Nyaya-Vaisheshika, and Mimamsa-Vedanta.

1. Samkhya (The School of Dualistic Realism)

Founded by the ancient sage Kapila, Samkhya is widely recognized as the oldest of the orthodox philosophical systems. It provides the foundational materialistic and metaphysical ontology for several other Indian schools, most notably Yoga, and heavily influenced the philosophical constructs found in the Mahabharata and the Bhagavad Gita.

Metaphysics and Ontology:
Samkhya posits a strict, uncompromising dualism, asserting that the universe consists of two ultimate, eternal, and entirely independent realities:

• Purusha: The principle of pure, transcendental consciousness. It is the absolute, passive, observing, and immaterial soul. Purusha is devoid of attributes, form, and agency; it is the silent witness to the cosmos. There is a plurality of Purushas, corresponding to individual souls.
• Prakriti: The primordial material matrix of the universe. It is active, unconscious, and constitutes the entirety of the physical and mental world. Prakriti is composed of three fundamental strands or Gunas (qualities), which are in a state of perfect equilibrium before creation: Sattva (representing illumination, harmony, and happiness), Rajas (representing action, passion, and movement), and Tamas (representing ignorance, inertia, and darkness).

The Evolution of the 25 Tattvas (Principles):
According to Samkhya, creation is not an act of a divine, conscious creator. Instead, it is a spontaneous evolutionary manifestation that occurs when the passive Purusha comes into mere proximity with Prakriti. This proximity upsets the delicate equilibrium of the three Gunas, triggering a cascading devolution of matter. This evolutionary process produces 25 Tattvas (elements or principles) that make up the known universe:
1. Purusha (The Transcendental Self)
2. Prakriti (The Unmanifest Primordial Nature)
3. Mahat or Buddhi (The Cosmic Intellect or discriminative intelligence, the first evolute of Prakriti)
4. Ahamkara (The Ego or principle of individuation, generating the sense of "I")
5. Manas (The central coordinating Mind, acting as both a sensory and motor organ)
6. 6-10. Jnanendriyas (The five sensory organs of knowledge: eyes, ears, nose, tongue, skin)
7. 11-15. Karmendriyas (The five organs of action: speech, hands, feet, excretory organs, reproductive organs)
8. 16-20. Tanmatras (The five subtle elements or potentials: sound, touch, form, taste, smell)
9. 21-25. Mahabhutas (The five gross elements: ether, air, fire, water, earth).

The Path to Liberation:
In the Samkhya framework, human suffering and ignorance arise when the pure consciousness (Purusha) falsely identifies itself with the ever-changing material intellect, mind, and ego (Prakriti). The soul forgets its liberated nature and feels bound by the physical world. Liberation (Kaivalya) is therefore not a physical relocation to a heavenly realm, but a profound cognitive realization—the absolute discriminative knowledge (Viveka) that the soul is entirely distinct from matter.

2. Yoga (The School of Mysticism and Discipline)

While Samkhya provides the intricate theoretical and psychological framework of the universe, Yoga, systematized by Sage Patanjali in the Yoga Sutras, provides the rigorous practical, physiological, and meditative methodology required to actualize liberation.

Core Philosophy:
Yoga completely accepts the dualistic epistemology and metaphysics of Samkhya—including the evolution of the 25 Tattvas—but crucially introduces a 26th entity: Ishvara (a Personal God). In Patanjali's Yoga, Ishvara is not necessarily the creator of the universe, but rather an omniscient, eternally liberated, and supreme soul who serves as a divine teacher and an anchor for meditation. This addition transforms Yoga into a theistic adaptation of the Samkhya philosophy.

The Ashtanga Path (The Eight-Fold Discipline):
The fundamental goal of Yoga is defined as Chitta Vritti Nirodha—the complete cessation of the modifications or fluctuations of the mind. To achieve this ultimate stillness, Patanjali prescribed a highly structured eight-fold path (Ashtanga Yoga):
1. Yama (Universal ethical restraints: non-violence, truthfulness, non-stealing, celibacy, and non-possessiveness).
2. Niyama (Personal observances and discipline: purity, contentment, austerity, self-study, and surrender to God).
3. Asana (Physical postures designed to create bodily stability and health for prolonged meditation).
4. Pranayama (Regulation and control of the vital breath or energy).
5. Pratyahara (The deliberate withdrawal of the senses from external, worldly objects).
6. Dharana (Focused concentration of the mind on a single point or object).
7. Dhyana (The unbroken, continuous flow of meditation on the object).
8. Samadhi (The ultimate state of blissful absorption, where the distinction between the meditator and the object of meditation dissolves, leading to liberation).

3. Nyaya (The School of Logic and Epistemology)

Founded by Sage Gautama (author of the Nyaya Sutras), Nyaya stands as the premier system of Indian logic. It operates on the foundational premise that nothing should be accepted on blind faith, tradition, or dogma; instead, all philosophical propositions must be subjected to a rigorous framework of critical inquiry and logical proof.

Epistemological Framework:
Nyaya is renowned for its exhaustive analysis of Pramanas (the valid instruments or sources of knowledge). To ascertain the truth of any phenomena, Nyaya strictly accepts four Pramanas:
1. Pratyaksha (Direct perceptual knowledge obtained through the senses and the mind).
2. Anumana (Inference based on a prior perception and an invariable concomitance, or Vyapti, between two phenomena).
3. Upamana (Comparison or analogical reasoning, gaining knowledge of an unknown object by recognizing its similarity to a known object).
4. Shabda (The verbal testimony of reliable authorities, which includes the infallible Vedas).

Nyaya developed a highly sophisticated five-step syllogism for formal logical deduction (Anumana), which became the standard for all philosophical debates in India. The steps are: the proposition to be proved (Pratijna), the reason (Hetu), an example establishing the universal rule (Udaharana), the application of the rule to the current case (Upanaya), and the final conclusion (Nigamana). For instance: The hill has fire (proposition); because it has smoke (reason); wherever there is smoke, there is fire, like in a kitchen (example); the hill has smoke (application); therefore, the hill has fire (conclusion).

Liberation (Apavarga) in Nyaya is attained by acquiring valid knowledge (Prama) of reality and eradicating false knowledge (Aprama), which destroys the cycle of desires, aversions, and subsequent rebirth.

4. Vaisheshika (The School of Logical Atomism)

Founded by Sage Kanada, Vaisheshika is an ancient system of physics, mechanics, and metaphysics. It attempts to objectively classify the entire universe into logical categories, acting as a highly realistic and proto-scientific philosophical framework. Over time, its physical theories were integrated with the logical frameworks of Nyaya to form a syncretic school of logical atomism.

Metaphysics and the 7 Padarthas:
Vaisheshika postulates that the physical cosmos can be entirely reduced to irreducible, indestructible, and indivisible particles called Paramanu (atoms). To systematically categorize all of reality, the school identifies seven Padarthas (categories of existence):
1. Dravya (Substance): The fundamental substratum of the universe. There are exactly nine substances: earth, water, fire, air, ether, time, space, soul, and mind. The first four are atomic and physical; ether, time, space, and soul are all-pervading and eternal; the mind is atomic but immaterial.
2. Guna (Quality): 24 specific attributes that inherently reside within substances (e.g., color, taste, magnitude, intellect, pleasure, pain).
3. Karma (Action): Physical movement, categorized into upward motion, downward motion, contraction, expansion, and locomotion.
4. Samanya (Generality): Universal properties shared by multiple entities (e.g., the "cowness" shared by all cows).
5. Vishesha (Particularity): The unique, ultimate characteristic that distinguishes one atom or soul from another (this concept gives the school its name, Vaisheshika).
6. Samavaya (Inherence): The inseparable, intimate relationship between a substance and its qualities, or a whole and its parts.
7. Abhava (Non-existence): Added by later scholars to complete the ontological picture, it is categorized into antecedent non-existence (before a pot is made), subsequent non-existence (after a pot is smashed), mutual non-existence (a cow is not a horse), and absolute non-existence (a square circle).

5. Purva Mimamsa (The School of Vedic Ritualism)

Founded by Sage Jaimini, Mimamsa (meaning deep reflection or critical inquiry) acts as the theological defense of the early Vedic ritualistic tradition, focusing exclusively on the Karma Kanda (the action-oriented portion of the Vedas).

Core Philosophy:
The school vehemently argues that the Vedas are eternal, unauthored (Apaurusheya), and absolutely infallible in all matters. It views religion not as a mystical connection with a creator God, but as the strict, flawless execution of moral duties (Dharma) and fire sacrifices prescribed in the Vedic texts. The Mimamsakas believe that the universe operates on an autonomous, mechanical moral law. When a ritual is performed with absolute phonetic perfection and procedural accuracy, it generates an unseen, magical metaphysical force called Apurva. This Apurva guarantees that the desired result—whether earthly prosperity, victory in war, or passage to heaven—is granted automatically by the universe. Because the rituals themselves compel the universe to act, classical Mimamsa renders a supreme creator God entirely unnecessary, bordering on functional atheism.

6. Uttara Mimamsa / Vedanta (The School of Upanishadic Non-Dualism)

Representing the philosophical climax of Indian spiritual thought, Vedanta (meaning the "end of the Vedas") rejects the rigid ritualism of Purva Mimamsa and shifts the analytical focus entirely to the philosophical treatises of the Upanishads, which form the Jnana Kanda (knowledge portion) of the Vedas. Compiled systematically by Sage Badarayana in the foundational text known as the Brahma Sutras, Vedanta investigates the ultimate nature of Brahman (the infinite, absolute, formless reality) and its complex relationship with the Atman (the individual soul).

The Evolution of the Sub-Schools of Vedanta:
Due to the profound brevity and complexity of the Brahma Sutras, subsequent medieval scholars interpreted the ontological relationship between Brahman, the physical world (Jagat), and the individual soul (Jiva) in vastly different ways. This interpretative divergence led to the creation of several powerful sub-schools, which form a critical component of the UPSC Mains syllabus:

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Part II: The Heterodox Schools (Nastika / Sramana Tradition)

The middle Gangetic plains during the 6th century BCE were a hotbed of intellectual ferment. The transition to an agricultural economy, the emergence of early state formations (Mahajanapadas), and the rise of trade guilds created a social environment that questioned the utility of expensive Vedic animal sacrifices and the deeply entrenched caste hierarchies perpetuated by the Brahmin class. In response, wandering ascetics, collectively known as Sramanas, propagated heterodox philosophies that completely rejected the authority of the Vedas, democratizing philosophy and spirituality.

7. Charvaka / Lokayata (The School of Radical Materialism)

Attributed to the ancient, somewhat mythical sage Brihaspati, Charvaka represents the most radical, purely materialistic, and skeptical school of Indian philosophy. The term Lokayata translates to "ideas derived from common people," indicating its populist appeal against clerical elitism.

Epistemology and Metaphysics:
Charvaka epistemology is famously austere: it completely rejects all sources of knowledge except direct sensory perception (Pratyaksha). It even rejects logical inference (Anumana), arguing that one can never establish an invariable, universal connection between two things without a leap of faith. Since entities like the soul, heaven, hell, karma, and God cannot be perceived by the human senses, Charvaka dismisses them entirely as elaborate fictions fabricated by the priestly class to extract wealth and maintain social control. Ontologically, the universe is composed of only four perceptible elements: earth, water, fire, and air. The fifth element, ether, is rejected because it cannot be seen or touched. Consciousness is not a spiritual entity but merely an emergent byproduct of these material elements combining in a specific proportion, much like the intoxicating power of liquor arises from fermented ingredients.

Ethics:
Its ethical philosophy is pure hedonism. It dictates that since death is the absolute end of existence and there is no karmic retribution in an afterlife, the singular rational goal of human life is the maximization of physical and mental pleasure and the minimization of pain.

8. Ajivika (The School of Absolute Fatalism)

Founded by Makkhali Gosala, who was a contemporary of both the Buddha and Mahavira, the Ajivikas were a prominent and highly influential ascetic order in ancient India.

Core Philosophy:
The central and defining doctrine of the Ajivikas is Niyati (absolute determinism or fatalism). They argued that the universe operates on an unalterable cosmic blueprint. Human free will is an illusion, and the concept of Karma—the idea that present actions dictate future outcomes—is a complete fallacy. Every sentient being must endure a rigidly pre-destined number of rebirths across vast cosmic cycles before achieving automatic liberation, regardless of their moral conduct. Despite their fatalism, which seemingly negates the need for effort, Ajivika monks practiced extreme, rigorous asceticism.

9. Jainism (The School of Ascetic Pluralism)

Jainism, an ancient Sramana tradition revived and popularized by the 24th Tirthankara, Vardhamana Mahavira, presents a highly sophisticated metaphysical and ethical framework. It emphasizes severe asceticism, extreme non-violence (Ahimsa), and the sanctity of all life forms.

Ontology:
Unlike Buddhism, Jainism asserts the existence of an eternal, individual soul (Jiva). However, it uniquely posits a panpsychic view of the universe: absolutely everything—including microscopic life forms, rocks, water drops, and fire—possesses a soul. The physical, non-living world is categorized as Ajiva. The soul is inherently pure and omniscient but is bound to the cycle of rebirth by subtle, material karmic particles that physically adhere to the soul due to worldly passions and violent actions. Liberation requires shedding this karmic matter through austere physical discipline.

Epistemological Masterpieces:
Jainism's greatest contribution to Indian intellectual history is its doctrine of intellectual non-absolutism, designed to foster deep philosophical tolerance and mitigate dogmatism:

• Anekantavada (The Theory of Plurality): Reality is multifaceted, incredibly complex, and possesses infinite attributes. Because human comprehension is inherently limited, no single perspective can capture the absolute, comprehensive truth. This concept is famously illustrated by the parable of the blind men and the elephant, where each man perceives only a part of the truth.
• Syadvada and Saptabhangi Naya: This is the practical epistemological method used to express the reality of Anekantavada. It mandates that all declarative statements must be conditioned with the prefix "Syad" ("in a certain sense," "from a perspective," or "maybe"). The Saptabhangi (seven-fold predication) outlines seven logical possibilities for expressing the truth of any proposition, proving that binary logic is insufficient:

1. Syad-asti: In a certain sense, it is.
2. Syad-nasti: In a certain sense, it is not.
3. Syad-asti-nasti: In a certain sense, it is and is not (successively).
4. Syad-avaktavya: In a certain sense, it is indescribable (simultaneously being and non-being).
5. Syad-asti-avaktavya: In a certain sense it is, and it is indescribable.
6. Syad-nasti-avaktavya: In a certain sense it is not, and it is indescribable.
7. Syad-asti-nasti-avaktavya: In a certain sense it is, it is not, and it is indescribable.

10. Buddhism (The School of the Middle Way)

Founded by Siddhartha Gautama in the 6th century BCE, Buddhism emerged as a powerful counter-narrative to Vedic orthodoxy. It rejected both the extreme hedonism of the materialists and the severe bodily mortification practiced by the Jains and Ajivikas, instead advocating a balanced "Middle Path".

Core Metaphysics:
Buddhism fundamentally challenges the central Upanishadic notion of a permanent, eternal soul (Atman). Its ontology is governed by radical impermanence:

• Anatta / Anatman: The doctrine of "No-Soul". The individual ego or self is an illusion; a human is merely a temporary amalgamation of five aggregates (Skandhas): form, sensation, perception, mental formations, and consciousness.
• Kshanikavada: The theory of absolute momentariness. Everything in the physical and mental universe is in a perpetual state of flux. Nothing remains the same for two consecutive moments, much like the flame of a candle.

Pratityasamutpada (Dependent Origination) and the 12 Nidanas:
The cornerstone of Buddhist philosophy is Pratityasamutpada—the causal law that all phenomena arise in strict dependence upon preceding causes and conditions. Nothing exists independently or permanently. This causal chain of suffering that binds sentient beings to Samsara (the cycle of rebirth) is detailed sequentially in the 12 Nidanas (Links):
1. Avidya (Fundamental Ignorance of the true nature of reality).
2. Samskara (Volitional formations, intentions, or karmic tendencies).
3. Vijnana (Consciousness).
4. Nama-Rupa (Name and form; the manifestation of the psycho-physical organism).
5. Sadayatana (The six sensory bases, including the mind).
6. Sparsha (Sensory contact with the external environment).
7. Vedana (Feeling or hedonic sensation).
8. Trishna (Craving or thirst for pleasure and continued existence).
9. Upadana (Clinging or grasping at objects of desire).
10. Bhava (The process of becoming or worldly existence).
11. Jati (Rebirth into a new life).
12. Jara-marana (Old age, decay, sorrow, and inevitably, death).

The Four Philosophical Sub-Schools of Buddhism:
As Buddhism evolved chronologically, particularly making the transition from early Theravada (Hinayana) thought to the expansive Mahayana tradition, it fragmented into four highly sophisticated philosophical schools. These schools were dedicated to understanding the true nature of reality and human consciousness:

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Part III: Advanced Dynamics & Metaphysical Frameworks (UPSC Mains Focus)

To achieve mastery over the General Studies Paper I and the Philosophy Optional syllabi, aspirants must move beyond mere memorization and comprehend the cross-cutting epistemological, causal, and ontological debates that raged between these competing schools for centuries.

A. Epistemology: The Battle of the Pramanas

Pramana Shastra (the science of epistemology) deals with the valid instruments or means of acquiring knowledge. In ancient India, the validity of a philosophical school often rested entirely on which Pramanas it accepted and defended in public debates. The six major Pramanas are: Pratyaksha (Perception), Anumana (Inference), Sabda (Verbal Testimony/Vedas), Upamana (Comparison), Arthapatti (Postulation/Presumption), and Anupalabdhi (Non-perception/Absence).

The table below maps the acceptance of these instruments across the major schools, revealing a spectrum from radical empiricism to expansive traditionalism:

B. Theories of Causation (Karyakarana Vada)

The relationship between a cause and its effect dictates how a philosophical school views the creation of the universe and the ultimate nature of reality. Indian philosophy centers around three primary causal doctrines:
1. Satkaryavada (The Pre-existence of the Effect): Upheld by Samkhya and Advaita Vedanta, this theory argues that an effect is not a newly created entity, but rather, it already exists in a latent, unmanifested form within its material cause. For example, oil is already present in the sesame seed before pressing. This theory branches into two critical interpretations:

• Parinamavada (The Samkhya view): The cause undergoes a real, physical transformation to become the effect. Just as milk really transforms into curd, Prakriti really transforms into the physical universe.
• Vivartavada (The Advaita Vedanta view): The cause undergoes only an apparent or illusory transformation. The effect is merely a psychological superimposition on the cause. Just as a rope merely appears as a snake in the dark, the ultimate reality (Brahman) only appears as the pluralistic physical universe (Maya) without actually changing its fundamental nature.

2. Asatkaryavada / Arambhavada (The Non-existence of the Effect): Fiercely upheld by Nyaya and Vaisheshika. It posits that the effect does absolutely not pre-exist in the cause. Causation is the creation of a fundamentally new entity (Arambha). For example, a clay pot is a newly created object that is distinctly different from the raw clay particles that form it.
3. Pratityasamutpada (Dependent Origination): The Buddhist view of causation, which strikes a middle ground. An effect arises conditioned by a cause, but the cause is completely destroyed before the effect is produced. This enforces the Buddhist theory of universal momentariness and denies any permanent substance.

C. Theories of Error (Khyativada)

When a human being makes a cognitive mistake—such as mistaking a piece of shell on a beach for silver, or a rope in the dark for a snake—what exactly is happening in the mind? The Khyativada debates are central to Indian epistemology, determining how schools separate truth (Prama) from illusion (Aprama).

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Part IV: Synoptic Analysis for Civil Services Preparation

1. The Materialistic and Proto-Scientific Heritage:

A common Orientalist misconception is that ancient India was exclusively mystical, spiritual, and world-negating. However, critical analysis for Mains answers should spotlight the robust, secular, and scientific traditions inherent in Indian philosophy. Vaisheshika provided an early atomic theory of physics (Paramanu), Charvaka established strict empirical parameters, and early Samkhya proposed an evolutionary, atheistic model of the universe functioning through the dynamic tension of material properties (Gunas). This demonstrates an advanced proto-scientific temper that thrived alongside, and often challenged, orthodox theology.

2. The Democratization of Philosophy and Society:

The emergence of the Sramana traditions (Buddhism, Jainism, Ajivika) constituted a massive socio-political democratization of philosophical thought. While Upanishadic knowledge was largely restricted to elite male Brahmins and conducted exclusively in Sanskrit, the heterodox sects shattered these barriers. By preaching in vernacular languages like Pali and Prakrit, and admitting women and lower castes into the monastic orders (Sangha), these schools fostered an egalitarian ethos. Jainism’s Anekantavada also laid the earliest intellectual foundations for religious tolerance and freedom of expression.

3. The Evolution from Intellectualism to Mass Devotion:

The chronological evolution of the Vedanta sub-schools reflects a deliberate historical shift to make salvation accessible to the masses. Adi Shankara's Advaita (8th century) was highly intellectual, demanding severe cognitive effort, strict morality, and asceticism to realize non-dualism. In contrast, scholars like Ramanuja (12th century), Madhvacharya (13th century), and Chaitanya recognized the sociological need for an emotional connection with the divine. By establishing Vishishtadvaita and Achintya Bheda Abheda, they integrated philosophical rigor with emotional surrender (Bhakti), laying the direct theological groundwork for the medieval Bhakti Movement that swept across the subcontinent.

4. Imperial Patronage and Philosophical Flourishing:

The philosophical evolution of India was heavily influenced by state patronage. The Mauryan Empire, particularly under Bindusara and Ashoka, championed the Ajivikas and early Buddhists, aiding the institutionalization of Sramana sects. Later, the Gupta Period (c. 4th–6th Century CE)—often termed the Golden Age—saw the massive revival of Brahmanical scholasticism. It was during this era that the orthodox Shad Darshanas (particularly Nyaya and Samkhya) were codified into formal Sutras under royal patronage. Similarly, King Harshavardhana heavily patronized Mahayana Buddhism, supporting the great university of Nalanda where Yogacara and Madhyamika scholars refined Buddhist logic.

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Quick Revision Summary & Bullet Points

For rapid recall during Prelims and last-minute Mains revision:

The Core Division:

• Orthodox (Astika): Accept the epistemological authority of the Vedas. Includes 6 schools (Samkhya, Yoga, Nyaya, Vaisheshika, Mimamsa, Vedanta).
• Heterodox (Nastika): Reject Vedic authority. Includes Charvaka, Jainism, Buddhism, Ajivika.

The Six Orthodox Schools (Shad Darshana):

• Samkhya: Founded by Kapila. Dualism of Purusha (soul) and Prakriti (matter). Atheistic origins. Identifies 25 evolutionary Tattvas.
• Yoga: Founded by Patanjali. Practical, meditative application of Samkhya. Introduces Ishvara (God). Features the 8-fold path (Ashtanga).
• Nyaya: Founded by Gautama. Focuses on logic and epistemology. Accepts 4 Pramanas (Perception, Inference, Comparison, Testimony). Employs a 5-step syllogism.
• Vaisheshika: Founded by Kanada. Physics and Atomism (Paramanu). Classifies the universe into 7 Padarthas (categories like Substance, Quality, Action).
• Purva Mimamsa: Founded by Jaimini. Focuses on the ritualistic portion of the Vedas (Karma Kanda). Believes the Vedas are eternal and rituals automatically yield results via the magical force of Apurva.
• Uttara Mimamsa (Vedanta): Founded by Badarayana. Focuses on the philosophy of the Upanishads (Jnana Kanda). Deals with the relationship between Brahman and Atman.

Vedanta Sub-Schools (Crucial for Matching Questions):

• Advaita: Adi Shankara (Absolute Non-dualism; World is Maya).
• Vishishtadvaita: Ramanuja (Qualified non-dualism; Soul is part of God; emphasizes Bhakti).
• Dvaita: Madhvacharya (Strict Dualism; Soul and God are totally and eternally separate).
• Shuddhadvaita: Vallabhacharya (Pure non-dualism; World is real; Pushti Marg).
• Dvaitadvaita: Nimbarka (Dualistic Non-Dualism).

The Heterodox Schools:

• Charvaka (Lokayata): Pure materialism. Founder Brihaspati. Accepts only Perception. Hedonistic ethics. Rejects the soul and the afterlife.
• Ajivika: Founder Makkhali Gosala. Absolute determinism/fatalism (Niyati). Rejects free will and Karma.
• Jainism: Founder Rishabhanatha / Mahavira. Believes everything has a soul. Famous for Anekantavada (multiple aspects of truth) and Syadvada / Saptabhangi (7-fold conditional predication).
• Buddhism: Founder Siddhartha Gautama. Rejects the eternal soul (Anatta). Focuses on Pratityasamutpada (Dependent Origination) and the 12 Nidanas (Wheel of Life causing suffering).

Buddhist Philosophical Sub-Schools:

• Vaibhashika: Direct Realism (Hinayana).
• Sautrantika: Representational Realism (Hinayana).
• Yogacara: Subjective Idealism / Mind-Only (Mahayana).
• Madhyamika: Anti-foundationalism / Emptiness / Sunyata (Mahayana; Nagarjuna).

Key Metaphysical Concepts:

• Satkaryavada: The effect pre-exists in the cause (Samkhya, Advaita Vedanta).
• Asatkaryavada: The effect is a completely new creation (Nyaya, Vaisheshika).
• Khyativada: Theories of cognitive error (e.g., Anirvacaniyakhyati of Advaita says the illusory snake is "indescribable" - neither real nor unreal).