In short, could your mind be so utterly irrational that that you're mistaken about the most basic questions of what you yourself know or think? It's far from a

In short, could your mind be so utterly irrational that that you're mistaken about the most basic questions of what you yourself know or think? It's far from a purely hypothetical scenario. After all, while dreaming we often follow nonsensical or self-contradictory chains of reasoning while thinking they make perfect sense – hence the term "dream logic". There are ways to try to identify that you're dreaming, and you can train yourself to use them more consistently, but they're far from perfect. Sometimes it just won't occur to you to do a dream test, and sometimes you'll fool yourself into thinking you passed the test. In my opinion, the only real solution is a pragmatic one. You can never be certain that you currently have any degree of rationality, and so you can never be truly certain about anything, period. However, you may as well assume you're rational for the purpose of making decisions. After all, if you're currently 100% irrational, then you're going to make 100% nonsensical decisions, and that's all there is to it. It doesn't really matter what you believe or disbelieve, so it doesn't hurt to falsely believe that you're rational. And there no point hedging on any action on the chance that you're being irrational, because the idea that "if i'm irrational, it's best to take/not take action X" is itself validated by rationality. That said, there are degrees between complete rationality and complete irrationality. In dreams you're often still partly rational, and you can also get a sort of replica of rationality by training yourself to follow specific thought patterns during times when you are mostly rational (i.e. awakeness). So it is theoretically possible to hedge based on the possibility that you're dreaming – albeit not very useful, since making bad decisions in a dream doesn't usually have any serious long-term effects. However, if you want to narrow things down to more specific possibilities than "I'm dreaming" – as you get to scenarios in which you're hypothetically being less and less rational, it becomes less and less useful to hedge on those scenarios.