ScholasticRealist wrote:

In discussing direct realism, I've maintained that a person cannot be deceived by his sensory perceptions. . . . My friend has pointed out that senses can be defective.

Frankly, I think you both have it backwards. 
I think you need to distinguish between sensation (e.g. seeing a red patch in one's visual field and having the feeling of a smooth cool surface in one's fingers) and sensory perception (e.g. perceiving an apple in one's hand).

We don't normally (arguably ever) experience mere isolated sensations (bare "sense data" or "raw feels" with no perceptual "interpretation"), but I think it's clear that a mere sensation can't be mistaken or deceptive. A perception, however, is a judgment (or at least very much like one), and it can be mistaken: we can think we're perceiving an apple when we're not. The intellect may be involved, but it may not; non-rational animals can make perceptual errors too, as e.g. when a dog sees its reflection in the water and drops the bone it's holding in order to go after that other one.

That seems to be roughly where you're headed with this:

ScholasticRealist wrote:

Or, should I just say that the senses report what they report, and that the deception would only occur if I judged my perception to be a true picture of the world's colors?

I'd say that's very much in the right direction. I'd carry on and acknowledge perception itself as at least a kind of proto-judgment.

Last edited by Scott (7/27/2015 7:06 pm)

seigneur wrote:

The connection of the channels is a judgement in the mind (conscious or subconscious), not in the senses.

For example, when a dog barks, our eyes see the dog, but they don't hear anything. The ears hear barking, but they don't see anything. Thus, even such a seemingly common-sense thing as a barking dog is a mental judgement with inherent subjectivity. It's not perfectly objective sense-data.

Exactly. Aquinas postulated/acknowledged a "common sense" (not what we mean by the term today) that "assembled" our sensory input into perceptual experience.

In view of the OP's reasons for raising the question, though, I should add that I don't think this view poses any threat to direct realism. First, on a Thomistic view of causation and perception, the color of the apple really is "in" the apple; at an absolute minimum, it's there as an effect that is virtually present "in" its cause. (I would even say with Anna Marmodoro that all the colors the apple may appear to be are really present "in" it.) Second, direct perceptual realism with respect to e.g. an apple requires that we be directly aware of the apple, not of one or another of its accidents, and I think that's the case on the Thomistic account.

The possibility of error is just that. Sure, we may think we're perceiving an apple when we're not, but the possibility of error presumes that there's such a thing as getting it right. And even when we misperceive, we're perceiving something; we're just mistaken about what.

I don't want to "intellectualize" the process too much; I think we do something in perception that non-rational animals don't do. But I think we have to recognize that there's such a thing as "perceptual judgment" even though its exercise doesn't require possession of an intellect. If that makes it merely "proto-judgment" for non-rational animals, then so be it. 

Last edited by Scott (7/28/2015 11:13 am)