|The first thing is that it's not necessary that I (or anyone) must accept this argument, as presented from the paragraph Bob posted. Basically, I hold my own counsel. (Separate from that, though, it is fun to unpack an argument to see how one element follows another.) I trust my senses AND trusting my senses is compatible with the evidence that my senses are fallible. My basis for understanding this is biological, so whether the above argument that Bob posted is true or false or in between doesn't touch what I already have learned from experience and evidence:|
Human visual physiology works by detecting photons (down to the level of a photon). The wavelength determines the color of light, the amount of photons determines the intensity/saturation (of light). That's my direction connection to reality-- light hitting my rods and cones. From there the information is taken to the visual centers in the brain to be processed. But along this pathway, we have a blind spot called the optic nerve. We get around that by constantly moving our eyes all over the place-- the only time we may see a blind spot is when we don't move our eyes enough. We "see" optical illusions-- and that is the result of the brain "filling in" visual information received when photons hit our eyes. We get around that by learning about what role the brain has in processing visual information. We may see a stick that looks bent when half of it is in water, but that is because of the way light (photons) behaves-- called refraction-- in water than it does in air.
It is possible to have our eyes to be healthy, but still be blind, seeing double, blacking out, etc.-- results of brain injury, physiological problems/responses, tumors, etc. However, we have more than one sense organ; more than one way of knowing the world-- it isn't just visual. So even if vision isn't reliable, a person still has touch, hearing, tasting, balance, proprioception, etc.
It is this that allows me to trust all my senses as my only way of knowing the world, yet also know that they have variable limitations. It's the combination of them that allows me a direct, individual understanding of the world; even if I am nearsighted, my hearing, visceral sensations, and touch are more sensitive. I do trust whatever I can see, and I trust that with glasses or contacts, the gradation of "flawed" is much lessened-- simply by the evidence provided when I wear my glasses versus not. When I don't wear corrective gear, I use my sense of touch and hearing more acutely-- this also happens when I am in a dark environment. For me, "flawed" does not necessarily connect to "unreliable", because due to the many complex systems that a human being is made of, there are alternative pathways to knowledge that can be strengthened and compensate for a less-than-normal ability.
One source that is unreliable does not mean it is necessarily useless. That source can very well be partially reliable or partially trustworthy, such as a dictionary. This can also be true of humans-- a person may speak falsely about one topic due to a multitude of factors (such as limits to a person's knowledge about a topic, bias, personal experience, etc.), but not about another topic. But, then, is this person the only person/object that one has to use as a source? Therefore, Bob, if you find the argument you posted lacking in something, it is not beyond you or any human to use a plurality of pathways for the goal of understanding. I find that it is within an individual's choice to find someone(s) who "fills in the gaps" for you in a way that elicits understanding, you filling in the gaps yourself, and/or, better yet, you creating your own argument for yourself. :)