Two Truths Doctrine

The two truths doctrine in Buddhism differentiates between two levels of truth in Buddhist discourse, a relative, or commonsense truth, and an "ultimate" truth or highest spiritual truth. It is used to avoid confusion between doctrinally accurate statements about the true nature of reality (e.g., there is no "self") and practical statements that make reference to things that, while not expressing the true nature of reality, are necessary in order to communicate easily and help people achieve enlightenment (e.g., talking to a student about "himself" or "herself"). While this division, particularly when referred to as the "satya-dvaya", is often associated with the Madhyamaka school, its history is quite extensive. Casual readers of Buddhist thought have often used the ideas of the two truths to erroneously identify Buddhism as being Transcendental in nature, and thereby identify its doctrines with Plato or Kant.

Canonical use
Two pairs of terms are used in the Pali Tipitaka. One pair is nītattha (Pali; Sanskrit: nītārtha, "of plain or clear meaning" (Monier-Williams)) and neyyattha (Pali; Sanskrit: neyartha, "(a word or sentence) having a sense that can only be guessed" (Monier-Williams)). These terms were used to identify texts or statements that either did or did not require additional interpretation in order to be made clear and/or non-contradictory and/or doctrinally accurate in a strict sense; a nītattha required no explanation, while a neyyartha text might mislead some people unless properly explained. (McCagney, 82)


 * There are these two who misrepresent the Tathagata. Which two?  He who represents a Sutta of indirect meaning as a Sutta of direct meaning and he who represents a Sutta of direct meaning as a Sutta of indirect meaning.
 * &mdash; Anguttara Nikaya I:60 (Jayatilleke, 361, in McCagney, 82)

The other pair is saṃmuti (Pali; Sanskrit: saṃvṛti; Pali = "common consent, general opinion, convention" (PED), with same meaning in Buddhist Sanskrit) and paramattha (Pali; Sanskrit: paramārtha, "ultimate"). These are used to distinguish conventional or common-sense language, as used in metaphors or for convenience's sake, from language used to express higher truths directly.

The term vohāra (Pali; Sanskrit: vyavahāra, "common practice, convention, custom" is also used in more or less the same sense as samuti.

In the canon, the distinction is not made between a lower truth and a higher truth, but rather between two kinds of expressions of the same truth, which must be interpreted differently. Thus a phrase or passage, or a whole sutta, might be classed as neyyattha or samuti or vohāra, but it is not regarded at this stage as expressing or conveying a different level of truth.

There is a canonical assertion that "truth is one" that might be held to conflict with a systematic assertion that there is a bifold distinction of truths. 

Theravāda commentarial tradition
The Theravādin commentators expanded on these categories and began applying them not only to expressions but to the truth then expressed.


 * The Awakened One, the best of teachers, spoke of two truths, conventional and higher; no third is ascertained; a conventional statement is true because of convention and a higher statement is true as disclosing the true characteristics of events.
 * &mdash; Khathāvatthu Aṭṭha kathǎ (Jayatilleke, 363, in McCagney, 84)

Further developments in Nikaya Buddhism
The Prajnāptivāda school took up the paramārtha/saṃvṛti distinction, and extended the concept to dharmas (metaphysical-phenomenological constituents), distinguishing those which are tattva (real) from those which are purely conceptual, i.e., ultimately nonexistent, "prajnāpti".

Madhyamaka
The distinction between two truths (satyadvayavibhaga) is of great importance for the Madhyamaka school, as it forms a cornerstone of their beliefs; in Nāgārjuna's Mūlamadhyamakakārika, for example, it is used to defend the identification of pratītyasamutpāda with śūnyatā.


 * The Buddha's teaching of the dharma relied on two truths,
 * The common truth of the world (lokasaṃvṛtisatya) and what is ultimately true (paramārthasatya).


 * They who do not know the division of the two truths
 * Do not know the deep reality of the Buddha's instructions.


 * The ultimate is not taught without resorting to the conventional (vyavahāra);
 * Without having gotten to the ultimate (paramārtha), nirvana cannot be approached.
 * &mdash; MMK 24:8-10