As interdisciplinary work inquires into the scope and content of the right to freedom of thought, we confront two crucial questions; for the purposes of this legal right, what should qualify as thought and what makes thought free? This chapter draws upon philosophical and psychological literature to suggest answers to these questions. First, we argue that thought does not only occur in a forum internum inside our heads. We propose that the right to freedom of thought should recognise and protect two types of what we call forum externum thought. Type 1 is ‘extended thought’. This occurs when we extend our mind using features of our body or environment, such as diary use and internet search (under certain circumstances). Type 2 is ‘thoughtspeech’. This occurs when we speak with others to think aloud together. We propose Type 1 and Type 2 forum externum thought should receive absolute protection only when they are employed for the purposes of self-government and truth-seeking respectively. We then turn to the question of what makes thought free. Here we focus on how the ‘trust and glue’ criteria for the extended mind can inform our consideration of what should count as impermissible alteration of extended thought. We conclude by pointing to the need for future transdisciplinary work to support the development of this right.