Write a short note on Vyāpti.

Vyāpti, a concept in Indian logic (Nyāya), refers to the universal concomitance or pervasion between the hetu (reason) and the sādhya (probandum or subject) in an inference (anumāna). It signifies the invariable relationship between the reason and the subject, where the presence of the reason invariably entails the presence of the subject. Vyāpti is a fundamental principle in Nyāya epistemology, serving as the basis for valid inference.

For example, in the inference "Wherever there is smoke, there is fire," the presence of smoke (hetu) invariably indicates the presence of fire (sādhya). This relationship of invariable concomitance is known as vyāpti.

Vyāpti is established through observation and generalization based on empirical evidence. Nyāya philosophers emphasize the importance of rigorously establishing vyāpti through observation, comparison, and analysis of numerous instances. Once vyāpti is established, it forms the basis for valid inference, allowing one to draw conclusions about unobserved or unknown phenomena based on known facts or observations. Thus, vyāpti plays a crucial role in Nyāya epistemology, facilitating the acquisition of knowledge through inference.