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Essays on seeing a red tomato, Parmenides, and the Phaedo


To: Stuart B.
From: Geoffrey Klempner
Subject: Essays on seeing a red tomato, Parmenides, and the Phaedo
Date: 11 April 2007 10:53

Dear Stuart,

Thank you for your email of 29 March, with your response to my comments on your essay, 'Is knowledge closed under known implication?', plus your new essay, 'What is the relation between perceiving the redness of a tomato and knowing that the tomato is red?', your second email of 29 March with your piece on Parmenides, and your email of 1 April with your piece on Plato's Phaedo.

Is knowledge closed under known implication?

I think that the appearance of disagreement is partly explained by the fact that you and I are initially thinking of different 'paradigm cases' of third-person attribution of knowledge. (1) My paradigm is where I am fully satisfied that P is the case, and my question is whether Smith's belief that P amounts to knowledge. (2) Your paradigm is a situation where I am looking to Smith for guidance on the question of P, and it is up to Smith to assure me that he does really know, and up to me to satisfy myself that his assurance is trustworthy.

1. What it takes to 'satisfy' me that P is the case depends on context. But that is factored out when I ask whether Smith knows that P. I am starting from P. That is a given, so far as I am concerned. The only question for me is whether there is any reason to deny that Smith's belief that P amounts to knowledge.

2. On the other hand, if I am not sure whether P, and Smith tells me that he knows, it seems that in order to satisfy me that his claim is justified he needs to give reasons for P. In evaluating these reasons as being sufficient for knowledge, I cannot have less information than Smith. - That is, unless we accept 'knowledge by testimony' as a valid route to knowledge in its own right. In that case my reasons justifying belief that P will differ from Smith's. My knowledge, in this example, relies on deference to the 'expert'.

However, the only way that such a scenario as (2) can arise is if Smith is able to persuade me, by giving other examples which I can evaluate independently. There can be a chain of experts, each validating the next, but ultimately, there is no way to dispense with cases like (1).


I'm not sure that you have taken the best approach to this question.

Whether or not there are 'at least eighteen fundamentally different ways of understanding, and hence describing, the relation between perceiving the redness of a tomato and knowing that the tomato is red' is a matter of debate. Imagining myself as an examiner, the thought that I am about to be made to wade through all the various permutations and combinations is enough to put anyone off.

The question is about the relation between perception and knowledge and also, arguably, about the relation between sensation and perception. What you are being asked to do is use the given example as a way to get into these issues, rather than to laboriously canvass all the possibilities and draw the conclusions as they apply to the example.

I would start with the question why we need a concept of perception. What is the point of distinguishing knowledge gained through inference to the best explanation, and knowledge gained through perception? Is there any difference, ultimately? How would you argue with someone who said that in so-called cases of 'perception' we are really inferring to the best explanation but unaware that we are doing this? Is perception just a species of belief/ judgement, or is it something more?

You say, 'Perceiving is automatically and unavoidably believing in a causal manner that is pre-cognitive and (mostly) beyond our control.' This seems the right thing to say, but still leaves open the question whether perception IS the belief or whether, alternatively, perception is a sui generis cognitive state which naturally gives rise to a particular kind of belief.

We agree about the rejection of the sense datum theory of perception. However, there is more to the question than this. After getting rid of indirect realism and phenomenalism, we are still left with different possible views on the nature of perception.


Taken out of context, your interpretation of Parmenides does not seem unreasonable. It is the sort of thing Karl Popper would do (see his enthusiastic essay, 'Back to the Presocratics' in 'Conjectures and Refutations' which you would probably enjoy). You've made things much easier for yourself by positing a 'vision' we would readily recognize. But how do you know that this was what Parmenides 'saw'? how would you respond to the challenge that attributing the vision to Parmenides is anachronistic?

We only have the preserved fragments to go by. You have provided an explanation, but one which is strongly underdetermined by the textual evidence.

What we do have in addition - which you take no account of - is the reactions of other Presocratic philosophers and these are very instructive: the debate with Melissus over the finitude or infinity of what is; Empedocles theory of four elements which acknowledges the impossibility of 'existence change' but allows new properties to come into existence or go out of existence as a result of mixture/combination; Anaxagoras' rejection of Empedocles account on the grounds that Parmenides' argument applies to properties too, hence all properties already exist and only their relative predominance changes; and, finally, the atomists, who argue for independent nuggets of Parmenidean being, separated by gaps of 'what is not'.

On your theory, these other thinkers were blind to Parmenides' vision, reacting instead to the superficial logic of his arguments.

In an essay on Parmenides argument for 'What is', you would not be expected to talk about all these other philosophers. What you are expected to do, however, is to go by the available textual evidence. The evidence is, admittedly, mutilated, but the mutilation is far from random. These were the bits that writers at the time - who we may assume were in the best position to know - saw fit to quote as representing the core message or argument. I find that thought reassuring.

Just one example. You say on page 2, 'Note that this last phrase, "for thought and being are the same thing" - makes it quite evident that Parmenides is considering "existence" as inclusive of conceptual existence.'

It is far from evident that this is what Parmenides is saying in the quoted fragment. He is using the 'capacity to be thought' as a criterion for what can exist. That which cannot be thought cannot exist.

However, it turns out - when we follow the steps of the argument - that only one thing can be thought, 'It is.' To say that It is conceptual implies that it is NOT material. To say that it is material implies that it is NOT conceptual. But we cannot say or think 'not'. Therefore, we cannot truly say that It is either conceptual or material. Like the Presocratics, Plato took Parmenides' argument and made crucial changes which allowed him to say things that Parmenides would have rejected as unsayable.


You have provided an answer to a possible exam question, 'Assess the validity of Socrates' arguments for immortality in the Phaedo'. I have not checked, but I doubt whether you would get a question as general as this. You are more likely to be asked to pick one argument and comment on it.

In the dialogue, Socrates expresses considerable diffidence regarding these 'proofs', showing that Plato's intention was not so much to give a conclusive demonstration of the thesis of immortality but rather to convey his view of the nature of the soul as 'akin to the forms'. To me, this is the most interesting question.

There is also a reference to the Pythagorean view of the soul as an 'attunement' which I discuss in the Pathways unit on Pythagoras.

In what sense can the soul be a 'form' or 'like' a form? You say that Plato is presented with 'an unresolved difficulty. Either each soul is the Form of the life it activates, and there are therefore a multitude of "Forms of Life", or we all "participate" in a singular "Form of Life" and there is no longer any real meaning to the idea of the immortality of the soul.'

Plato clearly intended the former alternative. He is talking about personal survival. However, it could be argued that if this is the case, then the self cannot be a Form. A Form is capable, in principle, of multiple instantiation. That's just what distinguishes a Form from particulars. But the self is irreducibly particular.

The soul of SB reborn as TC is one and the same individual (leaving aside awkward questions about criteria for personal identity in the absence of psychological continuity). The form 'SB' instantiated on twin earth or in the next cycle of the universe is not SB but another individual who merely shares the properties of SB.

It was not until Leibniz that we find the ingenious theory that there cannot, in principle, be two SBs (theory of monads and the identity of indiscernibles) and therefore that there can be such a thing as an 'individual concept'.

All the best,