---
type: Concept
bundle: nyaya-vaisheshika
bundle_version: 0.9.0
id: hetu
title: Hetu / Liṅga
iast: Hetu / Liṅga
devanagari: हेतु / लिङ्ग
description: 'The probative reason or inferential mark: the feature whose presence signals the property to be established, valid only when it meets the required conditions (belonging to the subject, present in like cases, absent from all unlike cases); NOT merely ''the middle term'', NOT any correlated feature.'
darshana:
- Nyāya
- Vaiśeṣika
text_source: Nyāya Sūtra 1.1.34-35
tags:
- hetu
- linga
- reason
- mark
- nyaya
not:
- term: the middle term of a syllogism
  why: The middle term is a purely positional role in a formal figure. The hetu is a real property functioning as a mark, and it is valid only if it satisfies substantive epistemic conditions in the world (pakṣadharmatā, presence in the sapakṣa, exclusion from the vipakṣa). It is defined by those conditions, not by its slot in a schema.
  instead: 'Define the hetu as a mark that earns its probative force by meeting the trairūpya conditions: it is a property of the subject, found wherever the target is, and found nowhere the target is absent.'
- term: any feature that happens to be correlated with the conclusion
  why: A merely correlated feature is precisely what Nyāya rejects as a pseudo-mark. A feature that also occurs where the target is absent is savyabhicāra (deviating); one that occurs only where the target is absent is viruddha (contradictory). The theory exists to separate a genuine mark from a lookalike.
- term: a cause or a clue in the loose sense
  why: Hetu is a technical role in inference, not causation in general. Smoke infers fire though smoke does not cause fire; the tie that matters is invariable concomitance (vyāpti), not the causal direction. Reading hetu as 'cause' inverts many valid inferences.
related:
- /concepts/anumana.md
- /concepts/vyapti.md
- /concepts/hetvabhasa.md
- /concepts/panchavayava.md
timestamp: '2026-07-02'
okf_version: '0.2'
license: CC BY-SA 4.0
---

# Hetu / Liṅga -- हेतु / लिङ्ग

**Not:** the middle term, a correlated feature, a cause

## What It Actually Means

The hetu (reason), also called liṅga (mark), is the pivot of inference: the property that, once seen in the subject, carries the mind to the property being established. Its authority is conditional. The classical requirement is trairūpya, three marks of a good reason: the hetu must qualify the subject (pakṣadharmatā), must be present in at least one similar case where the target is known to occur (sapakṣa-sattva), and must be wholly absent from every dissimilar case where the target is absent (vipakṣa-asattva); later logicians add further conditions. A feature that fails any of these is not a weaker mark but a hetvābhāsa, a mere semblance of a reason. So the hetu is never just 'a term' or 'a correlation'; it is a property doing probative work under strict, world-involving conditions.

## Audience Metaphor

A password field accepts any string in the right position; that is the middle term. A key is different: it opens the lock only if its actual cut matches the actual pins. The hetu is a key, not a slot. Present the right-shaped mark and knowledge turns; present a lookalike that also fits the wrong doors and the tradition names it a counterfeit (a pseudo-mark), not a weak key.

## Citations

1. Nyāya Sūtra 1.1.34-35 -- see [references/nyaya-sutra.md](../references/nyaya-sutra.md)
2. Dignāga and the trairūpya doctrine, absorbed and debated in Nyāya; see Uddyotakara, Nyāyavārttika -- see [references/nyayavarttika.md](../references/nyayavarttika.md)
3. Annambhaṭṭa, Tarkasaṃgraha on the definition of hetu -- see [references/tarkasamgraha.md](../references/tarkasamgraha.md)
