Conventional truth is the everyday reality of life as it appears to us. Ultimate truth is the nature of things as they really are. This risks being an oversimplification but expresses the essence of the Two Truths doctrine which permeates Mahayana Buddhism.
The historical Buddha lived during a time in which various ascetic movements were staking their claims against the norm. He was familiar with at least some of the Brahmanical terms used by the traditional philosophers of his days. He embraced the escape from suffering as his primary goal. He presupposed the cycle of rebirth in his teachings. By all accounts in the thousands of pages of the original teachings, the Buddha was a product of a Vedic environment.
The empirical truth of the world as it appears (Samvriti-Satya) is the truth of experience. The appearance, smell, and feel of a tree. The attraction and love felt toward another person. The measurements, calculations, materials, and effort needed to launch a rocket into orbit. These are expressions of empirical truth. Ultimate truth (Paramartha-Satya) exists beyond categories, linguistic appellations, and sensory experiences. Ultimate truth is the truth of the world as it is grasped only through intuition. The “transcendental” conception of the Two Truths might have roots in the Lokottaravada, an offshoot of the Mahasanghika, school of pre-Mahayana Buddhism.
In the words of Shantideva, the author of The Way of the Bodhisattva:
Relative and ultimate,
These the two truths are declared to be.
The ultimate is not within the reach of intellect,
For intellect is said to be the relative.1
A profound, concise exposition of the two types of truth is found in Nagarjuna’s Fundamental Wisdom of the Middle Way. In his famous work on the all-permeating aspect of emptiness, Nagarjuna goes so far as to say that anyone who has not grasped the two truths and how they relate to one another has not truly understood the Buddha’s teachings.2
Sanskrit: Saṃvṛti-satya, Paramārtha-satya
1The Way of the Bodhisattva, 137.
2Fundamental Wisdom of the Middle Way, 298-299.