Liberty of thought is the first liberty that the Preamble to the Constitution of India aims to secure. Yet, one finds no mention of ‘thought’ as one of the protected freedoms under Part III of the Constitution, which safeguards fundamental rights. This chapter takes the first steps to address this riddle and locating the normative foundations for the right. It argues that while the Preambular ideal itself is insufficient to confer a substantive right, its role in judicial interpretation, along with the interrelationship between fundamental rights, provides a robust normative foundation for the right to freedom of thought in India. Specifically, the chapter discusses the development of the right to mental privacy in the context of brain-reading in Selvi, and later in Puttaswamy. The right to (mental) privacy read into dignity by the Supreme Court of India already takes steps towards constructing a forum internum, and on the other hand, the challenge of the vulnerability of the legal subject becomes evident in the context of the right to freedom of conscience. Regarding the absolute nature of the right, this chapter argues that only as a Preambular ideal is the liberty of thought absolute within the Indian legal framework.