TrueTemp
A man has a device implanted in his brain that reliably produces true temperature beliefs. He doesn't know the device exists. Does he know the temperature?
Keith Lehrer introduced the TrueTemp case in 1990 to test reliabilist theories of knowledge. The case asks whether a belief formed by a reliable process counts as knowledge when the believer has no access to that process and no way to justify the belief from the inside.
Lehrer, K. (1990). Theory of Knowledge. Westview Press.
The scenario
Norman has had a device implanted in his brain. The device reliably causes him to form true beliefs about the current temperature. When it's 72 degrees, he thinks "it's 72 degrees." He's always right.
He has no idea the device exists. The belief simply appears in his mind, seemingly from nowhere. He has no thermometer, no memory of checking the weather, no reason to trust this particular belief over any other. From his perspective, it's a groundless hunch.
Why reliabilists say he knows
Reliabilism, developed most influentially by Alvin Goldman, holds that a belief counts as knowledge when it is produced by a reliable cognitive process. The process need not be transparent to the believer. What matters is that it works.
By this standard, Norman knows the temperature. The device is reliable, the belief is true, and that's enough. Demanding that Norman also have an internal justification adds a requirement reliabilism explicitly rejects. Reliability is the whole story.
Why internalists disagree
Internalist theories hold that justification must be accessible to the believer. You can only be justified in a belief if you have some reason, accessible from your own perspective, to think the belief is true.
Norman has no such reason. He's in exactly the position of someone guessing randomly, except that he happens to always guess right. If justification requires internal access to grounds for belief, Norman has none. His beliefs are lucky, not justified, even if they're reliably produced.
The case cuts at the heart of the debate: is knowledge a matter of how your beliefs are caused, or a matter of whether you have good reasons you can actually point to?
Discussion questions
- If a process reliably gives you correct beliefs, does it matter that you do not know why?
- Is self-awareness of how you are forming a belief necessary for that belief to count as knowledge?
- Can you think of a reliable belief-forming process you use that you do not fully understand?
Take it to the dinner table.
Get 3 thought experiments for memorable conversations, designed for dinner, with friends, at events, or anywhere small talk has gone on too long.