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This was a fun discussion, but I feel that it was hobbled by misunderstandings of one another’s language. Forget what’s “really out there”, I’m not quite sure what we were “really talking about”!

For instance, when Dan asserted that vision must be accurate to some degree due to evolutionary pressure, he used the example that a patch of color that is bridge-shaped to a human must actually be a bridge (and not more river) or the human in question is unlikely to pass on their genes. Professor Grobstein responded that a water-strider can cross water and is not held by that same scruple. This argument comes from a difference in meaning, not perception. It does not address the accuracy of vision in Dan’s example, only whether the interpretation of that visual input is universal. Both the human and the water strider accurately detect the water and the bridge and what affects their action and situation is their species. My recent Philosophy of Mind class has given me some structure with which to look at these conversations and has also lead me to worry that we have neglected the implied content of language, e.g. we are speaking of a human being viewing a bridge at a given time and place under conditions that the individual believes to be standard as compared to his general experience. These are the things that individuals raised in human society understand and accept that are not in the explicit things they say to one another, and must be considered in any examination of perception. These implied caveats would otherwise be identified as the error in perception, which brings us to the example of the chemist who labels colored flasks.

Did Professor Grobstein mean to question our use of labels to describe common perceptions? The word “red” may indeed be misapplied to an object emitting different wavelengths than the ones we commonly describe as red in a room saturated with colored light, but it is still possible to figure out what is happening there if we are fair to the chemist in the discussed scenario. Should we really deprive the chemist of access to different lighting, assume that the chemist has no peers or training that might enable them to recognize the error in color reporting, and so on?

Likewise, I do not see the connection in the ambiguous cases, where our visual perception does not match externally-recordable information about an object. This includes all of the animations and illusions which produced erroneous colors or movement when viewed by the human eye. Again, I am not convinced that this has meaning regarding “what’s really out there” other than to delineate limitations of the naked eye. It doesn’t feel like a good starting point for our eventual discussion of philosophical meanings and individual perspective, the Capital-T Truth. It presents a contradiction, for in being taught these illusions and visual artifacts we were in fact presented with an “objective” reality, or a “more objective” one. The woman is not spinning left or right, but the animated image is moving in a way such that our particular visual system can interpret it in that way. The checkerboard is not continuous through the shadow cast by the cylinder, those blocks are the same shade and our brain simply tells us they aren’t. In showing us that a particular instance of vision is flawed, we are given a more complete and correct understanding of it. How does that do violence to the idea of objectivity?

So, I don't object to the theme of progress – of having more things to know and having better ways to examine things. I believe that these examples unambiguously support that. What I do object to is the contention that there is a useful definition of “what’s really out there” that is also impossible to discover. If it is possible for something to affect us in any way, it must be detectable through its effects, even if in the slightest and least intuitive of ways. We could be brains in bottles, we could be holograms, or we could be made out of lots of tiny bees – but, until we can find a hint that those things aretrue, it is safe and expedient to accept the null hypothesis.