John M. Cooper, 'Plato on Sense Perception and Knowledge (Theaetetus 184-186)' in Fine's Plato 1.

• By the end of the article, Cooper thinks his article has identified what is important about the Theaetetus' rejection of perception as knowledge. Namely, it brings on the recognition that bare sensory awareness is different from sensory labeling, which is different from forming judgements of various sorts based on sense data. That is an advance on what we find in the Republic or Phaedo, and so Cooper thinks is a point in favor of his interpretations.
• Plato's argument that knowledge is not perception
• two prevailing interpretations:
• The objects of perception are just not the sort of things we have knowledge of or can have knowledge of (i.e. we can't perceive the forms)
• Plato never formulates this in the Theaetetus itself. In other dialogues, we are given reasons to suspect this is what he thinks, however.
• Cooper points out that in the Tht. all we see is the mind applying common conceptions (existence, sameness, unlikeness, likeness, identity, etc.) to perceptions, but nothing is said about their status or how they are applied.
• Sensation and judgement are distinct (179c), but Plato does not make that clear via the forms: he uses the common conceptions of the mind.
  
• The thinking we do about perceptions is knowledge, not the perceiving or the contents of perceptions themselves.
• Merely using senses is not enough for knowledge
• Plato seems to want to limit perception to the proper objects of the senses (see Frede's article too here).
• So what is Plato saying about perception?
  
• The mind interprets the sense data.
• The mind sees things THRU the sense organs.
• The senses themselves are not aware of the data they collect?
• The mind is aware of it thru the senses.
• The mind can also apply "common conceptions" to sense data to judge that this data is like something or is different from something or is the same as something, etc.
  
• It makes judgements THAT something exists, is like, is different, etc.
• These judgements involve "common conceptions": i.e. things like sameness, difference, identity, beauty, goodness, oneness, etc.
  
• Plato does not discuss at all in the Tht. WHERE the mind gets the common conceptions from.
  
• Plato may differentiate between acts of perception of the mind and those of the body.
  
• So when he rejects the thesis that knowledge is perception, what is he rejecting?
  
• He probably rejects the purely bodily perceptual acts of the sense organs AND the act of labelling some given sense data as "blue" or "red" or "smelly" AND the mental act of perceiving "that there is blue", or "that this smells"
  
• We have to watch out for what he means when he says "perception is knowledge"
• At 186b11, he says the perceptual actions are common to humans, beasts, and day-old babies: that is mere sensory awareness without any labelling or judgement "that ..."
  
• If this is the sort of thing he means by "perception" in rejecting the thesis that perception is knowledge, then he is rejecting a minimal candidate for knowledge that few would claim is sufficient for knowledge.
• That candidate is something like merely the ability to sense anything without any capacity for judgement or reasoning about the data collected by the senses: that is what it seems that babies and beasts have.
  
• When he illustrates independent use of the mind "itself by itself" in contrast to perception, he uses exclusively the application of common conceptions as illustrations.
• At 185b and 186b, he says that we decide and investigate whether a color or sound is similar or not using our minds independently of the body.
• Alongside of that, he says we investigate whether things are bitter with our senses
• So senses can include the labels "bitter" or "red" or "smelly" and that does not involve use of the mind itself by itself.
  
• And it's not the use of labels such as "bitter" or "red" that he is rejecting when he rejects perception as knowledge.
• He means to reject "this is red" as a candidate for knowledge and accept "this red thing exists" or  "this red thing is similar to that" as candidates.
• He does that because the ones he accepts involve common conceptions.
  
• 185e 6 makes this most clear, when he concludes that there are some things the mind investigates by itself and others it does thru the bodily senses.
• So maybe he is rejecting everything short of that.
• Plato seems to differentiate between those processes that require a conversation of the mind with itself and those which do not.
• Mere recognition that red is present to the eyes does not require any identifiable thought: it seems to happen automatically without any conscious thought about it. It is sufficient merely to direct your attention to a stop sign and "that's red" pops to mind. No thought.
• But when we say "that stop sign is like the ones in Madagascar," we employ a concept "likeness" that requires the mind to "converse with itself"
• NOTE (this is Bailly's sceptical addition): this all may seem plausible, but think of certain processes that we make "automatic" by practice. For instance, the thought required to decide how much to turn the wheel of a car to get into that parking spot or how much pressure is required to brake by a certain point: we don't have a conversation with our mind to do such things. They are automatic.
• BUT they have not always been so: we started out driving having to think hard about all such things.
  
• Cooper suggests that in the "passive" occurrence of perceiving, and in the more active act of labelling something "red" or "tasty," as well as in the formulation of the judgement "that thing is red," we have all the evidence we need from the senses. IN CONTRAST, when we formulate a judgement that involves common conceptions, our evidence for judgements such as "that thing is as red as a cherry" or "that thing is tasty in a similar way to rhubarb pie," we have to consult evidence outside of our sense data.
  
• So perhaps going beyond sense data for evidence is the key difference between perception and thought.
• Next, Cooper says that Cornford misread the Theaetetus. Cooper seems to have a point. Cornford was so eager to find the Forms in the Theaetetus that he ignores the fact that even people who don't believe in Forms believe in things like equality, identity, existence, and so the mere presence of them in a theory of epistemology is not sufficient to see the forms. Cooper carefully points out that the Theaetetus never discusses the Forms qua Forms nor does Plato show any interest in where the "common conceptions" come from or what their nature is. Thus the Theaetetus is innocent of the Forms.
• Plato is interested in the difference between operations of the mind involved in perception and thought about perception, not in the Forms in the Theaetetus, Cooper concludes.
• Plato clearly thinks that any candidate for knowledge must "grasp being" and "grasp truth"
• What he means by that must be figured out by examining the account he has given of application of the common conceptions to sense data (i.e. he does not discuss it directly, so we have to look for evidence).
• Cooper comes up with two interpretations, both of which he thinks are plausible and cannot be rejected. He opts for the second one.
1. Perception is mere perceptual awareness and is not knowledge because it does not involve discursive thought.
2. Perception is perceptual awareness plus labeling of sense data, but it fails to be knowledge because such things cannot be independently verified and are not a matter for experts.
   
1. Perception is mere perceptual awareness and is not knowledge because it does not involve discursive thought.
• Thinking involves thinking that ... , namely it involves application of concepts to form thoughts that have propositional form or can be formulated into propositional form.
  
• This interpretation has the advantage that knowledge is the sort of thing that can be true or false, and that requires propositions.
• It fits with various things Socrates says, such as 186d2: "So there is no knowledge in the experiences we undergo, but rather in the reasonings we do concerning them":
  
• sense awareness is supposed to be purely passive, whereas labeling involves activity that can be called "reasonings."
• BUT this interpretation has disadvantages.
• namely, the idea that perception does not involve propositional content must somehow be found in the text of the Theaetetus to justify this interpretation.
• The only place Cooper can think of to find it is in the assertion that in perception we do not grasp being.
• "being" has apparently meant "existence" in the dialogue in its previous occurrences.
• that would mean that we cannot perceive existence with the senses, which seems right.
• but how does that imply that perception lacks any judgement or propositional content whatsoever?
• perhaps Plato thinks that any time we make judgements, we must either concomitantly make a judgement about existence or before we make any other judgements, we must judge existence.
• Cooper thinks that both of those are not good options. He does not say why. I guess it's just obvious. Maybe it is.
• but maybe "being" means not just existence, but any predicative use of the verb "be" to predicate something of an object. Namely, any judgement that says "X is Y"
• That would provide an easier and more defensible version of this interpretation.
• And Greek uses the same verb for existence and "X is Y"
• Still problematic, because the labeling process (saying "red" when you see red) is related as not involving any proposition. Not all concepts require "being" to be applied, perhaps
2. Perception is perceptual awareness plus labeling of sense data, but it fails to be knowledge because such things cannot be independently verified and are not a matter for experts.
• This interpretation has a lot going for it too.
• First, Cooper goes to look at a related matter, the refutation of Protagoras in which Socrates says that any predictions are not like other appearances, because after the time has passed by at which the predictions are supposed to occur, we can verify that they did (not) occur, and so there is room for being mistaken.
• Predictions involve expertise, in other words: the experts are right in their predictions (or right more of the time than non-experts).
• Just so, knowledge implies expertise for Plato, and perceptions are not the sort of thing that one can "correct": if one sees red and labels it "red," nothing can correct that (not even pointing out that the object is not 'really' red)
• So perception is not knowledge because it cannot be corrected, it cannot be subjected to evidence that is external to the perceiving agent.
• This interpretation uses clearly Platonic assumptions (knowledge is expertise) and is a philosophical advance.
• Whichever interpretation we follow, Cooper thinks his article has identified what is important about the Theaetetus' rejection of perception as knowledge. Namely, it brings on the recognition that bare sensory awareness is different from sensory labeling, which is different from forming judgements of various sorts based on sense data. That is an advance on what we find in the Republic or Phaedo, and so Cooper thinks is a point in favor of his interpretations.