In 2025, the UK's Technology Secretary was forced to hand over his conversations with ChatGPT. Most of us would feel unease at giving up our search histories, our notes, our late-night messages—yet the law treats all of it as data the state can demand, not thought it must leave alone. Psychologist and neuroscientist Simon McCarthy-Jones argues this rests on a mistake. We still imagine thinking happens sealed inside the skull, but we now think on our phones and through the machines we talk to. Some of what sits in our pockets is part of how we reason, remember and work things out, and it deserves the same protection as the thoughts in our heads. The law already treats freedom of thought as absolute. It should extend that protection beyond the skull: when what we type is genuinely exploratory and unfinished, the state should be no more able to read it than to reach inside our minds.

The law protects your body. It protects your property. It protects your speech. But does it protect something arguably more fundamental: your thoughts? This seems like a dry legal question that can be safely left to lawyers. But it isn’t, and it can’t. Law, claimed the legal philosopher H.L.A. Hart, is too important to be left to lawyers. Hart’s observation is particularly true when it comes to safeguarding thought, due to its centrality to human dignity, autonomy and the functioning of democratic societies.

The problem is that the law has a distorted image of thought. Its picture of thought is encapsulated in Rodin’s famous statue, The Thinker. Here, thought occurs inside a solitary figure, invisibly gestating beneath furrowed brows. This internalist conception of thought is intuitive and comes to us early. It is already grasped by four-year-olds, who understand there is a thing called thinking, distinct from talking, which happens inside people’s heads.

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A society that punishes thinking in public will not produce better thinkers. It will only produce better liars, cowards and conformists.

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Yet, as philosophers and cognitive scientists have long argued, thinking also occurs outside our heads. It happens in notebooks, in marginalia, and under the crossed-out sentence; in online search queries, diagrams, and unsent emails; in voice notes, arguments, and in conversations in therapy rooms, classrooms, and on generative artificial intelligence (AI) platforms. We don’t always think and then express our thoughts. The expression can be the thinking.

Socrates is a better guide to thought than Rodin. Socrates viewed thinking as something that happens in dialogue, through questioning and answering. Following Socrates, the philosopher Agnes Callard calls the idea that thinking is something you can do by yourself a “solipsistic illusion.” Thinking, she argues, is something that happens through conversation, rather than being the activity of a “special being, the mind, that lives inside us.”

The law’s conception of thought is impoverished because historically it has drawn a neat line between thought and speech, then focused on protecting the latter. Discussions of free speech fill up volumes of legal cases and journals, whereas free thought is rarely mentioned. Such neglect made some sense when our thoughts appeared inaccessible. However, with the advent of neuro-technologies and the use of machine learning to infer what is going on inside people’s heads from the data they leave online, the situation changed. Our minds became leaky.