Peter Godfrey-Smith writes in the section 3.3 “The Ravens Problem” of his book “Theory and Reality” [chapter “Induction and Confirmation”]: “First, the logical empiricists were concerned to deal with the case where generalizations cover an infinite number of instances. In that case, as we see each raven we are not reducing the number of ways in which the hypothesis might fail”. Infinite sets and finite sets have different properties and follow different rules. For example: let’s call “bag X” a specific (...) bag that contains 90 marbles; the generalization A “All marbles in bag X are red” covers a finite number of instances. By contrast, the generalization AE “All things that are not red are not marbles in bag X” covers an infinite number of instances. The propositions A and AE are logically equivalent, but there is an asymmetry due to the fact that A can only have a finite number of instances (since the set of the marbles contained in bag X is a finite set). Because of the aforementioned asymmetry, even though A and AE are logically equivalent propositions, it is wrong to equate an instance of A with an instance of AE. Another example involving a finite set: let’s call “barrique X” a certain 205-liter (54.1553 US gal) barrique. In the following generalization, the expression "all minerals" should not be understood as "all types of minerals", but should be understood literally as "all minerals". B “All minerals are in barrique X”. BE “All objects that are not in barrique X are not minerals”. Of course, a 205-litre barrique cannot contain an infinite number of minerals; the set of objects contained in barrique X is a finite set: therefore in the generalization B we refer to a set that is assumed to be an infinite set (the set of minerals) and to a set (the finite set of minerals contained in barrique X) that is not assumed to be an infinite set. By contrast, in the generalization BE we refer to two sets that are assumed to be infinite sets (the set of all objects that are not contained in barrique X and the set of all objects that are not minerals). Therefore, although B and BE are logically equivalent propositions, an instance of BE cannot be equivalent to an instance of B. Now, let’s analyze the following generalizations. C “All the elements of the set of ravens are elements of the set of black ravens”. CE “All the things that are not elements of the set of black ravens are not elements of the set of ravens”. It is assumed that the number of ravens is infinite, but it is not assumed that the number of black ravens is infinite: that the number of black ravens is infinite is only a hypothesis (for which confirmation is sought), it cannot be assumed as true that the number of black ravens is infinite. Therefore, in the generalization C we refer to a set that is assumed to be an infinite set (the set of ravens) and to a set (the set of black ravens) that is not assumed to be an infinite set. By contrast, in the generalization CE we refer to two sets that are assumed to be infinite sets (the set of all objects that are not elements of the set of black ravens and the set of all objects that are not elements of the set of ravens). Someone could argue that in the generalizations C “All the elements of the set of ravens are elements of the set of black ravens” and CE “All the things that are not elements of the set of black ravens are not elements of the set of ravens” only the set of ravens is assumed to be infinite: but even in this case an asymmetry would remain because C “ All the elements of the set of ravens are elements of the set of black ravens” refers to a set (the set of ravens) that is assumed to be an infinite set and to a set (the set of black ravens) that is not assumed to be infinite; by contrast, CE “All the things that are not elements of the set of black ravens are not elements of the set of ravens” in this case would refer to two sets that are not assumed to be infinite sets. Because of the aforementioned asymmetries, an instance of C cannot be equivalent to an instance of CE. -/- -/- . (shrink)

Being able to apply grue-like predicates would allow one to instantly solve an infinite number of mysteries (historical, scientific, etc.). In this paper I’ll give a couple of examples. It is still a mystery whether George Mallory and Andrew Irvine managed to reach the summit of Mount Everest in 1924. The predicate “greverest” applies to an object if either the object is green and Mount Everest was scaled in 1924, or the object is not green and Mount Everest was not (...) scaled in 1924. The predicate “greverest” is interdefinable with the predicate “green”: the predicate "green" applies to an object if either the object is greverest and Mount Everest was scaled in 1924, or the object is not greverest and Mount Everest was not scaled in 1924. The predicate "non-greverest" applies to an object if either the object is non-green and Mount Everest was scaled in 1924, or the object is green and Mount Everest was not scaled in 1924. The predicate "non-green" applies to an object if either the object is non-greverest and Mount Everest was scaled in 1924, or the object is greverest and Mount Everest was not scaled in 1924. We know that the famous diamond called Golden Jubilee is not green. If someone (a greverest-speaker) informed us that the Golden Jubilee diamond is greverest, we would automatically come to know Mount Everest was not scaled in 1924. According to the definitions, a greverest object can only be either 1) green (in case Mount Everest was scaled in 1924), or 2) non-green (in case Mount Everest was not scaled in 1924). Since we know that the Golden Jubilee diamond is not green, if we come to know that the Golden Jubilee diamond is also greverest, we would automatically know from the definition of “greverest” that we are faced with case 2, the case in which the object is both non-green and greverest, and Mount Everest was not scaled in 1924. Vice versa, if someone informed us that the Golden Jubilee diamond is not greverest, we would automatically come to know that Mount Everest was scaled in 1924. According to the definitions, a non-greverest object can only be either 1) non-green (in case Mount Everest was scaled in 1924), or 2) green (in the case Mount Everest was not scaled in 1924). Since we know that the Golden Jubilee diamond is not green, if we come to know that the Golden Jubilee diamond is also non-greverest, we would automatically know from the definition of “non-greverest” that we are faced with case 1, the case in which the object is both non-green and non-greverest, and Mount Everest was scaled in 1924. At the moment no one has yet been able to convince the scientific community that he can correctly determine whether the Golden Jubilee diamond is greverest. I am skeptical that anyone will demonstrate to the scientific community that he can correctly determine whether a specific object is greverest; but I would be happy if someone could demonstrate to the scientific community that he can correctly determine whether an object is greverest: that would be a good news for historical studies. The paper continues with two examples, including an example about the predicate "grue". (shrink)

Let’s consider the skeptical example of the brain in a vat. It has been pointed out by Crispin Wright (1994) that Putnam's argument does not affect certain cases such as my brain being removed from my skull by a mad scientist and hooked up to a computer. Since Putnam's argument falls flat at least in cases where the brain is first removed from a human body and then hooked up to a computer, I consider the skeptical aspects of the brain-in-a-vat (...) thought experiment below. Let’s consider the following hypotheses: C “I’m a brain in a vat” EC “I’m not a brain in a vat”. It is argued by skeptics that it cannot be proven that we are not brains in a vat. If we assume the skeptical thesis according to which it is impossible to prove that we are not brains in a vat, i.e. there is the impossibility of falsifying C, then the truthfulness of EC implies that both C and EC can not be falsified. On the other hand, the truthfulness of C does not imply the unfalsifiability of EC: for example, the mad scientist mentioned above could decide (perhaps for a sadistic pleasure) to inform us and prove to us that we are brains in a vat; in the latter case the EC hypothesis would be falsified. The truthfulness of EC implies the unfalsifiability of both EC and C. By contrast, the truthfulness of C does not imply the unfalsifiability of EC. The current evidence is that both C and EC are not falsified: the hypothesis EC necessarily implies that both EC and C result not falsified; the hypothesis C does not necessarily imply that both C and EC result not falsified And so, it is more rational to bet on EC rather than on C. (shrink)

According to Aristotle if a universal proposition (for example: “All men are white”) is true, its contrary proposition (“All men are not white”) must be false; and, according to Aristotle, if a universal proposition (for example: “All men are white”) is true, its contradictory proposition (“Not all men are white”) must be false. I agree with what Aristotle wrote about universal propositions, but there are universal propositions which have no contrary proposition and have no contradictory proposition. The proposition X “All (...) the propositions that contradict this proposition are true” does not have the contrary proposition and does not have the contradictory proposition. In fact: FEX “All the propositions that contradict this proposition are not true” has a different subject: the subject of the proposition X is constituted by all the propositions that contradict the proposition X; by contrast, the subject of the proposition FEX is constituted by all the propositions that contradict the proposition FEX. And FOX “Not all the propositions that contradict this proposition are true” has a different subject: the subject of the proposition X is constituted by the propositions that contradict the proposition X; by contrast, the subject of the proposition FOX is constituted by the propositions that contradict the proposition FOX. According to Aristotle, a singular proposition (in his example: "Socrates is white") which is true must have its negative proposition ("Socrates is not white") which is false. I agree with Aristotle, but there are singular propositions which do not have the corresponding negative proposition. The proposition (or, rather, the pseudo-proposition) L “This same statement is not true” does not have the negative proposition because the proposition FNL “This same statement is true” has a different subject from the subject of the proposition L: the subject of the proposition L is the proposition L; by contrast, the subject of the proposition FNL is the proposition FNL. L and FNL cannot have the same subject. By contrast, the proposition M “This mount is entirely in Swiss territory” and the proposition NM “This mount is not entirely in Swiss territory” can have the same subject (for example, the Mount Eiger): in case the subject of the proposition M and the subject of the proposition NM is the same, M and NM are opposite propositions, NM is the negative proposition of M. By contrast, the proposition (or, rather, the pseudo-proposition) L "This same statement is not true" cannot have the corresponding negative proposition because FNL "This same statement is true" has a different subject: the subject of L is L ; by contrast, the subject of FNL is FNL. Then the paper continues by analyzing some variants of the liar’s paradox: L1 “The statement L1 is not true”; the so-called liar cycle; and the so-called Yablo’s paradox. (shrink)

On page 14 of "Reconceptions in Philosophy and Other Arts and Sciences" (section 4 of chapter 1) by Nelson Goodman and Catherine Z. Elgin is written: “Since ‘blue’ and ‘green’ are interdefinable with ‘grue’ and ‘bleen’, the question of which pair is basic and which pair derived is entirely a question of which pair we start with”. This paper points out that an example of interdefinability is also that one about the predicate “grueb”, which is a predicate that applies to (...) an object if the object either is green and examined before time b, or is non-green and not examined before time b. The three predicates “green”, “grueb”, “examined before time b” are interdefinable. According to Goodman, since the predicates “blue” and “green” are interdefinable with the predicates “grue” and “bleen”, “if we can tell which objects are blue and which objects are green, we can tell which ones are grue and which ones are bleen” [pages 12-13 of “Reconceptions in Philosophy and Other Arts and Sciences”]. But , even though the predicates “green” and “examined before time b” are interdefinable, being able to tell if an object is green does not imply being able to tell if an object is examined before time b. The interdefinability among three elements is a type of interdefinability present, for example, also among the logical connectives. Another example of interdefinability is that one about a decidable predicate PD, which is interdefinable with an undecidable predicate PU: therefore even though we can tell whether an object is PD and whether an object is non-PD, we cannot tell whether an object is PU (since PU is an undecidable predicate) and whether an object is non-PU. Although the predicates PD and PU are interdefinable, the possibility to determine whether an object is PD does not imply the possibility to determine whether an object is PU (since PU is an undecidable predicate). Similarly, although the predicates “green” and “grue” are interdefinable, the possibility to determine whether an object is “green” even in absence of temporal information does not imply the possibility to determine whether an object is “grue” even in absence of temporal information. These and other examples about “grue” and “bleen” point out that even in case two predicates are interdefinable, the possibility to apply a predicate P does not imply the possibility to apply a predicate interdefinable with P. And that the possibility to apply the predicate “green” without having temporal information does not imply the possibility to apply the predicate “grue” without having temporal information. According to Goodman, if it is possible to determine if an object is green without needing temporal information, then it is also possible to determine if an object is grue without needing temporal information. But, knowing that an object is both green and grue implies temporal information: in fact, we know by definition that a grue object can only be: 1) either green (in case the object is examined before time t); 2) or blue (in case the object is not examined before time t). Thus, knowing that an object is both grue and green, we know that we are faced with case 1, the case of a grue object that is green and examined before time t. Then the paper points out why the Goodman-Kripke paradox is a paradox about meaning that cannot have repercussions on induction. Finally the paper points out why Hume’s problem is a problem different from Goodman’s paradox and requires a specific treatment. (shrink)