My question was in reference to the first post shown above. Let me rephrase it. If one is not able to ascertain truth of one’s existence, ie. whether one is mere simulation in a simulated world, or not, how does one define concepts in relevant way?
IOW, in dream, we are not able to know that we are in dream. Can we define relevant concepts while in dream?
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Side note: I almost never remember dreaming. Whenever I have been in a dream that I can remember, I knew I was dreaming.
To answer your question, we do science. We look for regularities, make hypotheses, test those hypotheses, etc.
So, if we are in a simulation, and there are 'laws of physics' in that simulation, then by repeated observation and testing we can find approximations to those laws. We can still 'live our lives', 'drive our cars', etc.
And until there is some observation that requires something more, there is no reason to model something more. And that is perfectly good.
And then some dude offers you a red or blue pill and the observational evidence changes significantly.
One aspect of all of this is that observational equivalence is, for me, the same as equivalent.
So, if we are in a perfect simulation of the 'real world' and ALL observations are the same between the simulation and the 'real world', then what we see *is* the 'real world'.