The example ‘sound is eternal because it is caused’ represents which of the following Hetvabhasa?

The correct option is Viruddha.

In classical Indian logic (Nyaya philosophy), Hetvabhasa refers to a fallacy of inference. This occurs when the middle term (known as the hetu or reason) is defective and fails to validly establish the major term (known as the sadhya or the property to be proved).

Let us break down the components of the given statement, "Sound is eternal because it is caused":
1. Paksha (Subject / Minor Term): "Sound" (the object about which we are inferring something).
2. Sadhya (Major Term): "Eternal" (the property we want to prove about the subject).
3. Hetu (Middle Term / Reason): "Caused" (the reason provided to prove the property).

The fallacy of Viruddha (meaning "contradictory") occurs when the middle term (hetu) offered to prove the major term (sadhya) actually proves its direct opposite. In other words, the reason contradicts the thesis it is trying to support.

In this example, the reason given for sound being eternal is that "it is caused" (or produced). However, by definition, any object that is caused or produced has a beginning in time, making it temporary or non-eternal. Therefore, the reason "being caused" does not prove eternality; instead, it establishes the opposite (non-eternality). Because the reason contradicts the very claim it is meant to establish, it represents Viruddha Hetvabhasa.