Sunday, January 10, 2010

Thomas Reid and Acquired Perception

In his Essays on the Intellectual Powers of Man Thomas Reid maintains that experience can allow us to improve on our original perceptions, expanding the information available to us by way of our senses. In this category, Reid includes things from our ability to visually perceive tangible sizes and distances of objects (instead of simply the apparent sizes and distances of objects), to things like hearing the size of a bell and a butcher's ability to (visually) see how heavy some quantity of beef is. Reid labels this phenomenon "acquired perception", and takes the position that instances of it do not involve an act of reasoning, but he also indicates that he is not particularly concerned to argue that it is literally a form of perception — "Whether we call it judgment or acquired perception is a verbal difference" (EIP II.14, paragraph 37). Reid indicates that he is calling it "perception" simply to accord with what he regards as common usage of the term (EIP II.22, paragraph 31).

At the same time, one of the many interesting things that I think we can find in Reid's discussion of this topic is a decent way to defend his substantive underlying position (namely that beliefs arising from acquired perception are importantly different from both our original perceptions and from beliefs formed on the basis of reasoning). When Reid is concerned to show that many purported 'fallacies of the senses' are not really fallacies of the senses, he points out that when our acquired perceptions lead us astray, (for example, if one believes that there is a spherical object in front of them on the basis of seeing a really well-done painting of a sphere), we would not fault their faculty of vision (Reid's discussion of this point is from II.22. paragraph 31).

I think Reid could marshall this test in support of his position that acquired perception is not a product of reasoning. I am just as disinclined to consider someone who is taken in by a trompe l'oeil painting or the like a bad reasoner as I am to consider them someone with faulty vision. However, limiting our attention to this case might be considered stacking the deck in favor of Reid's position, since not all of his opponents would group visual perception of 3d shapes and distances as the same sort of acquired perceptions as a butcher's ability to estimate beef weight, or the like.

So, broadening the range of cases to consider, we can repeat the test. It is important to note that Reid's official position is that acquired perceptions are different in kind from both original perceptions and reasoned judgments, so, if no errors for any of the cases he is interested in fall under errors in the sensory or reasoning faculties, he is in good shape. I'm going to briefly run through the cases Reid gives in his earlier work (An Inquiry into the Human Mind on the Principles of Common Sense Chapter 6, section 20), and evaluate whether errors about such cases would have to be either sensory or reasoning errors.

"The shepherd knows every sheep of his flock, as we do our acquaintances, and can pick them out of another flock one by one. The butcher knows by sight the weight and quality of his beeves and sheep before they are killed. The farmer perceives by his eye, every nearly, the quantity of hay in a rick, or of corn in a heap. The sailor sees the burthen, the built and the distance of a ship at sea, while she is a great way off. Every man accustomed to writing distinguishes his acquaintance by their hand-writing, as he does their faces."

Thinking through these cases, I am also pretty sympathetic to the existence of a category of mistaken belief that is neither the produce of sensory error or the product of erroneous reasoning. Suppose a shepherd, attempting to identify which of the sheep among another flock are his sheep, misidentifies one of the other flock's sheep as his own. While such an error could be due to bad vision, or a bad inference ("one of my sheep has a misshapen ear, that sheep there has a misshapen ear, so, that is my sheep"), it also seems to me possible for the misidentification to occur without attributing the shepherd any visual faults and without any mistakes in reasoning (note: it might be that a shepherd who is prone to misidentify his sheep must be a bad reasoner to rely on his acquired perceptions of whether a given sheep belongs to his flock, but not necessarily in forming the bad judgments).

In fact, this might be one of the better ways to make the case for Reid's position that visual perception of properties like (3d) shape, size, and distance, are acquired perceptions like the farmer's ability to know by vision the quantity of hay in a given bale.

A few miscellaneous notes of things I didn't discuss: i) There are some important similarities between the position of Reid's that I am discussing and some of what Berkeley says about suggestion in the New Theory of Vision; I did not have space to go into those here, and also wanted to avoid saying potentially false things about Berkeley's views. ii) A more thorough discussion of this would definitely involve relating Reid's position to Locke's view about sensations being changed by judgment. iii) I would not be surprised if a better understanding of Reid's views on acquired perception help to shed some light on Hume's skeptical solution to the challenge of justifying causal inferences.

1 comment:

William said...

May what Reid is identifying is a kind of nonverbal thinking or reasoning that does not use the kind of logic that can be written, so it is neither vision alone nor logical thinking, but a nonverbal reasoning process.

This fits with what we know of how the brain works: much thinking does not use verbal logic.