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Unformatted text preview: P hase Two: The t ransit ion from “ Knowledge is of necessary t rut hs” to “ The objects one has knowledge about are invariable, fixed, permanent, unchanging - i .e., t he Forms.” Th is appears to be a different sort of fallacy: that of t ransferr ing a property of a proposit ion t o t he thing(s) the proposit ion is “about.” It’s not in general t rue t hat if p i s about x and p has property F , then x has F . (E.g., one may have a complex proposition about a simple object, a short proposition about a tall object, etc.) T wo comments on Plato’s move in Phase Two: i. Plato’s inclination to suppose that invariable objects are required as the things i nvariable (i.e., necessary) t ruths are about may have been fostered by his assimilation of propositional knowledge (“knowing that”) to knowledge by acquaintance (“knowing someone”). For the unalterability of the propositional object of knowledge seems to require a proposition that cannot ever fail to be t rue. And if one stresses the unalterability of the object of propositional knowledge and slides ( unwittingly) into thinking of it as knowledge by acquaintance, then it appears that an unalterable object that one can be directly acquainted with is required: a nonpropositional object of contemplation which always remains the same, etc. T he slide from knowledgep t o knowledgea is partially concealed by the fact that, in both cases, what is known can be described as a being, something that is. Cf. the p lausibili ty of both of principles (K v) and (K e): W hat you know p m ust be (= be t rue). W hat you know a m ust be (= exist). P lato’s move from invariable t ruths to invariable objects of knowledge may be made t o seem more plausible if one thinks of the bearers of t ruth-value - t he sorts of t hings that can be t rue or false - i n a non-standard way. T he standard way (nowadays): the bearer of t ruth-value (and hence the object of p ropositional knowledge) is what is expressed by a fully explicit declarative sentence, v iz., a proposition. Such things are either t rue (eternally) or false (eternally), and don’t go around changing t ruth-value. So the proposition that i t rained in Seattle on M arch 14, 1876 is, if t rue, t rue forever. I t won’t change in t ruth-value. I t does not d iffer at all in that respect from the proposit ion that 2 + 2 = 4. Thus, on this model it i s hard to see why necessity should have anything to do with f ix ity of t ruth-value. But suppose we t hink of the bearers of t rut h-value (i.e., the things our cognit ive states are about) as corresponding not to fully explicit declarat ive sentences, with all t he local and temporal parameters filled in (like “ It rained in Seatt le on March 14, 1876”) but as corresponding to what Quine calls “occasion sentences,” i.e., sentences l ike “ It’s raining.” Such sentences have implicit i ndexical elements (here, now, I, you, this, etc.) Such sentences are t rue on some occasions of utterance, and false on others. So if, on Monday, you have a belief that you express by saying “I t’s raining,” and, on Wednesday, I have a belief that I express by saying “I t’s raining,” you and I are in the same belief-state. The content of your belief looks (from the inside) exactly like mine. B ut we believe different propositions: what you believe is t rue, and what I believe is false. So if all one has to rely on is the contents of one’s mind, one’s belief-state, one cannot be guaranteed to arr ive at the t ruth. Here, then, is a cognitive state (belief) t hat can sometimes go wrong. B ut now contrast these (seemingly present tense) sentences:
o o “Two plus three equals five” (i.e., 2 + 3 = 5) “The sum of the interior angles of a t r iangle is equal to two r ight angles.” T hese cannot change in t ruth-value. And why is that? Contrast them with “I t’s r aining.” That can change in t ruth-value because the weather can change. But these m athematical statements have fixed t ru th-values because they are about objects t hat don’t change. The eternal t ruth of “3 + 2 = 5” is guaranteed by the fact that the entities involved, and the relations asserted to obtain among them, are not capable of changing in the respects needed to make the statement tu rn out to be false. P lato’s argument in Phase Two now seems much more plausible than it did before. But t here is still room to lodge a complaint: P lato has not allowed for the possibility of fixed and unchanging relationships a mong noneternal (contingent) objects. If there were such relationships, his demands for the objects of propositional knowledge would be met without the need for immutable objects of acquaintance (= the Forms). A re there such relat ionships? Consider these proposit ions:
• • • Zebras have st r ipes. Salt dissolves in water. Gold has atom ic number 79. These proposit ions seem to be invariably t rue, even though they are not about invariable objects. What makes “Zebras have st r ipes” invariably t rue is not the existence of an i nvariable zebra, but the fact that an invariable relat ionship exists among ordinary, variable, corrupt ible, f lesh-and-blood zebras. The discovery, exam inat ion, and explanat ion of such regularit ies in nature is the business of natural science, for which Plato makes no provision. His idea that things that can move and change are cognit ively unreliable, and cannot be known, has the consequence that n atu ral science is impossible ! For natural science - as Aristotle was quick to notice - “ must take for granted that the t hings that exist by nature are, either all or some of them, in motion (i.e., subject to change)” (Phys. 185a12-13). And physical science maintains that there can be invariable, necessary t ruths about changeable, corruptible objects. I nstead, Plato supposes that necessary t ruths are about Forms. If it really is invariably t rue t hat zebras have stripes, this is because of some invariable feature of the Zebra I tself, an i ncorruptible and eternal object of contemplation. Note that a consequence of the line Plato takes is that propositions that appear to be about sensible, spatio-temporal particulars turn out, if they are to be objects of knowledge, not to be about those things at all. Which is to say, our knowledge gets cut off from the world of experience. ...
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This note was uploaded on 01/31/2011 for the course PHYSICS 110 taught by Professor Staff during the Spring '09 term at UC Davis.
- Spring '09