In Buddhist philosophy, who is regarded as the teacher of the doctrine of shunyata, that is, the concept of emptiness or voidness in all phenomena?

Introduction / Context:
Shunyata, often translated as emptiness or voidness, is one of the central ideas in Mahayana Buddhist philosophy. The question asks which thinker is especially known for explaining this doctrine in a systematic and influential way. Knowing the key philosophers connected with different Buddhist schools and ideas is very important for history and religion questions in Indian and world examinations.

Given Data / Assumptions:
• The concept under discussion is shunyata, understood as emptiness or lack of inherent, independent existence. • The options list four well known religious and philosophical teachers from different Indian traditions. • The task is to identify who is most closely associated with teaching shunyata in Mahayana Buddhism.

Concept / Approach:
Shunyata in Mahayana Buddhism explains that all things arise due to causes and conditions and therefore do not have permanent, independent essence. This does not mean that nothing exists at all, but that phenomena are empty of fixed, unchanging self nature. Within Mahayana philosophy, the Madhyamaka school gave a detailed logical explanation of this idea. The founder and most famous philosopher of Madhyamaka is Nagarjuna, who used reasoning and analysis to show that all concepts are empty of inherent existence. Other thinkers in the options belong to different times and traditions, so they are not the main exponents of shunyata.

Step-by-Step Solution:
1. Identify which religious tradition emphasises the doctrine of shunyata. This doctrine is central to Mahayana Buddhism. 2. Recall the main philosophical schools of Mahayana, especially the Madhyamaka school, which focuses on the middle path and emptiness. 3. Note that Nagarjuna is widely regarded as the founder and chief philosopher of the Madhyamaka school. 4. Recognise that Nagarjuna wrote important works such as the Mulamadhyamakakarika, where he analysed concepts and showed their emptiness. 5. Compare this with the other options: Shankaracharya is a key figure of Advaita Vedanta, Harisena was associated with Gupta period court life, and Vallabhacharya is linked with the Vallabha sect and Bhakti tradition. 6. Therefore the thinker most directly associated with shunyata in Buddhist philosophy is Nagarjuna.

Verification / Alternative check:
A quick cross check is to match each name with its main contribution. When revising, students usually learn that Nagarjuna is connected with emptiness, Shankaracharya with non dual Vedanta, and Vallabhacharya with Krishna Bhakti in the Pushtimarg tradition. Only Nagarjuna fits the requirement of this question. This independent check supports the conclusion that Nagarjuna is the correct answer.

Why Other Options Are Wrong:
Shankaracharya: A major philosopher of Advaita Vedanta in Hinduism, he taught non dual Brahman, not specifically the Buddhist concept of shunyata. Harisena: Known as a court poet and officer under Samudragupta, he is not famous for any doctrine of emptiness. Vallabhacharya: A Bhakti saint who taught Shuddhadvaita and devotion to Krishna, not the Mahayana Buddhist idea of shunyata.

Common Pitfalls:
Many learners confuse different non dual teachings and think that any teacher of non dualism must also be teaching shunyata. However, Advaita Vedanta and Madhyamaka Buddhism, while having some surface similarities, are different traditions with different ultimate claims. Another common error is to choose a name that is more familiar, such as Shankaracharya, even when the concept clearly belongs to Buddhism. Careful reading of key words like shunyata and correct association with Mahayana Buddhism can prevent such mistakes.

Final Answer:
The doctrine of shunyata in Mahayana Buddhist philosophy is especially associated with Nagarjuna.