More on the same topic
I would disagree that ‘truthness’ (not to be confused with ‘truthiness’ ;] ) is not a physical property. All existing properties are ultimately physical. The truth of a statement does require a far more complex instrument to determine than the wetness of water, I’ll admit, but that doesn’t mean that it’s somehow beyond measurement and experiment.
‘Understanding’ involves processes which I do not personally understand, but just as many things previously thought to be mystical or non-physical have been shown to be explainable via physical processes and entities, I am confident that ‘understanding’ (and ‘consciousness’) will also be so shown.
“All existing properties are ultimately physical.”
I respectfully disagree, and for this reason. You are stating an article of faith, or perhaps a conclusion of metaphysics, but not a conclusion of science. If you know, not merely opine, that all statements can be reduced to statements about physical properties, then this knowledge is necessary and logical, not contingent. You are not uttering a conclusion proved to you by an empirical investigation. There is nothing you looked at in a telescope or microscope which taught you this idea.
If all properties were ultimately physical, the statement, “all properties are ultimately physical” could not be true, because it could be made false by altering a physical property.
Do you understand? Physical properties are contingent, not necessary. Twice two is necessarily four; it is four under all times places and conditions. The hue of a billiard ball is contingent. The same ball can be painted black on Tuesday, but repainted on Wednesday, so that it is yellow.
So if “all properties are ultimately physical” is a statement about material properties, as “the ball is painted black”, then something could be done– a reorganization of brain atoms or something of the sort, let us call it The White Event — to make it a true statement that “not all properties are ultimately physical.”
Now, given that, how do you know that we do not live in a post-White Event universe?
Out of all possible combinations of matter and energy the universe could possibly contain, how do you know this one we actually inhabit at this period in cosmic evolution is one where it happens to be the case that all properties are ultimately physical?
Is there any arrangement of matter and energy even theoretically possible such that the statement, “all statements are ultimately about physical properties” happens to be false in that time and place or under those circumstances? If your answer is “no”, I will refer you to Karl Popper. Any statement that cannot be disproven in an experiment is not scientific.