# Theaetetus (Plato)



## RamistThomist (Feb 15, 2021)

Plato returns to his criticism of Protagoras’s claim that man is the measure of all things. Granted that such an argument is wrong (and silly), we explore the nature of knowledge and why it can’t be sense impression.

Theaetetus has just come back from the Sophists who argue that knowledge = sense perception. The larger context is Protagoras’s claim that “man is the measure of all things.” We will call this claim (P). We will distinguish this from Theaetetus’s claim that knowledge is perception, called (T).

Socrates asks him that if (T) is true, then knowledge must also be perceiving, to which Theaetetus agrees. If this is true, then a thing’s appearing-to-me must also be a thing’s being or existence. Our claim now entails that such knowledge is unerring (since it is connected with being). This, however, is manifestly false. Case in point: we perceive things in dreams, but no one thinks dreams are real.

Theaetetus retreats from this claim and attacks from the Heraclitean point of view that “motion is the source of being.” Flux, not stability is primary. There is no self-existent thing. Everything is becoming and in relation. He has the nice phrase “Partisans of the perpetual flux.” Indeed, we can’t even say man or stone, but only an aggregate of x. This is word-for-word Karl Marx (Marx, Theses on Feuerbach, Thesis VI).

Let’s return to (P). If it is true, then there is no reason to believe that Protagoras (or the modern university professor) is correct. If knowledge is sensation, and I can’t discern another man’s sensation, and yet Protagoras purports to be true, then why prefer him to anyone else? This was the first response to postmodernism long before postmodernism came on the scene.

Another problem: I can have knowledge from memory, yet memory isn’t a sense.
Another problem: I can have knowledge of abstract entities and categories, yet these are present to the senses.

Let’s return to the Heraclitean claim. If nothing is at rest, and everything is supervening upon everything else, then every answer is equally right, since all we have are moving targets.

There is yet another diversion where Socrates explains that the soul perceives some things by herself and others by means of bodily organs. The soul has something like “wax” in it that handles the impressions. If a soul is deep and virtuous, then the impressions sink to the heart of the soul.

The dialogue ends with discussions of justified, true belief.

Arguably the most important of his “epistemology” dialogues, it is somewhat a difficult read as Socrates goes through numerous diversions.

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## Pergamum (Feb 15, 2021)

I really had trouble reading this one and I wondered why Plato did not directly appeal to the Forms? Any ideas?

And in the end Plato does not even give a definition of knowledge, does he? He just refutes other arguments and proves what knowledge is not. Am I remembering it correctly?

p.s., I think you forget to write "Not" here:
"Another problem: I can have knowledge from memory, yet memory isn’t a sense.
Another problem: I can have knowledge of abstract entities and categories, yet these are [NOT] present to the senses."

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## RamistThomist (Feb 16, 2021)

Pergamum said:


> I really had trouble reading this one and I wondered why Plato did not directly appeal to the Forms? Any ideas?
> 
> And in the end Plato does not even give a definition of knowledge, does he? He just refutes other arguments and proves what knowledge is not. Am I remembering it correctly?
> 
> ...



The Forms are more metaphysical, whereas this is mainly on epistemology.

He doesn't define knowledge. This is one of his "aporetic" dialogues. I think one of the reasons he doesn't define knowledge is that he anticipates the Gettier problem. Traditionally, knowledge = justified, true belief. Gettier poked holes in that as inadequate, and I think Plato suspected something like that.

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## Pergamum (Feb 16, 2021)

So how do you define knowledge?


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## RamistThomist (Feb 16, 2021)

Pergamum said:


> So how do you define knowledge?



Warranted, True Belief. Plantinga.

Knowledge as justified true belief (K = JTB), the standard account, says justification is necessary for warrant. I must satisfy some epistemic duty. Before I can ever say I know something, I must first satisfy certain internal criteria and provide evidence for my claim. That's not so much wrong as it is unrealistic.

Edmund Gettier suggested a number of scenarios that show where someone can know something yet not really have justification. A fourth criterion is needed. For example, I look at a field in the early morning fog and see what I think is a sheep. As it happens, it wasn’t a sheep but a wolf in sheep’s clothing. Unbeknownst to me, there was indeed a sheep in the field behind the wolf. Technically, I was correct. I saw something in the field that I thought was a sheep. It was true belief and I was justified in holding it, yet it wasn’t knowledge

Warrant, or externalism, by contrast, notes that many people have knowledge of situations_ s…z_ without being able to give ultimate justifications for their knowledge. They would say, rather, with Thomas Reid and Alvin Plantinga, “ Any well formed human being who is in an epistemically congenial environment and whose intellectual faculties are in good working order will typically take for granted at least three things: that she has existed for some time, that she has had many thoughts and feelings, and that she is not a thought or feeling” (Plantinga 50).

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## Pergamum (Feb 16, 2021)

BayouHuguenot said:


> Warranted, True Belief. Plantinga.
> 
> Knowledge as justified true belief (K = JTB), the standard account, says justification is necessary for warrant. I must satisfy some epistemic duty. Before I can ever say I know something, I must first satisfy certain internal criteria and provide evidence for my claim. That's not so much wrong as it is unrealistic.
> 
> ...


Interesting. Now I understand why you are a teacher. Thanks.

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