Step 1: Understanding Vijñānavāda.
Vijñānavāda is also known as the Yogācāra school. It is based on the "consciousness-only" doctrine.
Step 2: Concept of Vijñaptiḥ.
This school posits that external objects do not exist in themselves. All that we perceive are "vijñapti-mātratā," meaning "representations of consciousness."
Step 3: Analysis of options.
- (1) Nityatā: Buddhism adheres to anityatā (impermanence), not nityatā (permanence).
- (2) Śūnyatā: This is the doctrine of the Madhyamika school (Nāgārjuna).
- (3) Bāhyārthatā: Vijñānavāda rejects this concept (external reality).
- (4) Vijñaptiḥ: This is entirely correct, as it is the core principle of Yogācāra/Vijñānavāda.
Step 4: Conclusion.
Therefore, the correct answer is Vijñaptiḥ.