The possible world in which I have slippers on is not the one in which I have slippers off. Whether you like it or not, this is not a contradiction. — Banno
The modal logic is consistent, as Kripke and others have shown in their considerations of possible world semantics. — Banno
But without the metaphysical baggage you attach. A=A is valid. It is a necessary truth. When you say stuff like — Banno
Again, no, since the actual world is a possible world. That's been explained to you before. — Banno
Anyway, I hope it is clear to others that Meta's account is quite at odds with Kripke's, — Banno
Yes, it's consistent because they violate the law of identity, as I described. — Metaphysician Undercover
My bolding.Quantified Modal Logic—which combines individual quantifiers and modal... is sound and complete with respect to constant domain semantics, in which each possible world has precisely the same set of individuals in its domain. — SEP
Here's a tree proof:The law of identity is not valid. If you think it is, then show the logic which proves it. — Metaphysician Undercover
and here, again:It is as if a 'possible world' were like a foreign country, or distant planet way out there. — p.174
Of course there is an actual world. It's one of the possible worlds.There is no actual world, so how do you propose that I decide which of the possibilities to believe as the truth? — Metaphysician Undercover
Which returns to I think a major bone of contention in Kripke’s thesis, with respect to classes of statements of knowledge and of metaphysics, where he says, pg 177, “Now I hold that neither class of statements is contained in the other”. — Mww
The main point is that it is not trivial that just because such a statement is necessary it can be known a priori.
Of course, for Gödel the truth of such statements was relatively trivial - they said they were true, being of the rough form "This statement is true but unproven". The Goldberg Conjecture works as an example of a potential Gödel statement that is not quite so obvious - it's what such a statement might look like, intuitively true, true in every actual calculation, and yet unproven to be true. It becomes unclear what it might be to claim it is true a priori....even if everything necessary is a priori in some sense, it should not be taken as a trivial matter of definition. It is a substantive philosophical thesis which requires some work.
Heat is necessarily the motion of molecules. The sensation of heat is not......
But this does not undermine the broader case that sometimes if A=A, then ☐A=A. — Banno
It's consistent yet violates the law of identity?
Well, if it violates the law of identity, then it is by that very fact not consistent. — Banno
Here's a tree proof:
https://www.umsu.de/trees/#A=A — Banno
Of course there is an actual world. It's one of the possible worlds. — Banno
Saul Kripke described modal realism as "totally misguided", "wrong", and "objectionable".[27] Kripke argued that possible worlds were not like distant countries out there to be discovered; rather, we stipulate what is true according to them. — https://en.wikipedia.org/wiki/Modal_realism
Then comes:"But, all we need to talk about here is this: Is everything that is necessary knowable a priori or known a priori?" — Banno
Since it is a mathematical statement, if it is true, then it is true in any possible world - it is necessarily true. — Banno
Since we do not have a proof, we do not know if the conjecture is true. Hence we do not know a priori that the conjecture is true. — Banno
It becomes unclear what it might be to claim it is true a priori. — Banno
However, the law of identity doesn't show one way or another that heat is necessarily the motion of molecules, rather than heat is the Eiffel Tower, for example. — RussellA
I don't follow that. I don't see how molecules could exist but not their movement.Heat, temperature and energy are concepts and don't ontologically exist in the world — RussellA
Sure.This does not literally mean that knowledge ontologically exists in the world. — RussellA
Not so sure. Seems to me it means that the average movement of the molecules of one object has increased. That's a statement about how stuff is.if someone says that heat has been transferred from one object to another, this does not literally mean that heat ontologically exists in the world. — RussellA
I don't agree."Heat is necessarily the motion of molecules" cannot literally be true — RussellA
Banno, consistency is a relation between the axioms or premises employed. — Metaphysician Undercover
Same problem. Possible worlds are stipulated, not recognised. The actual world is a possible world. The alternative would be to claim that the actual wold is impossible.How would you reconcile these two — Metaphysician Undercover
So... we know stuff only by induction or by deduction?From a few instances of a posteriori proofs is developed a principle. For any instance other than from experience, in which the principle is the ground, the proof must hold as it did a posteriori. Otherwise, it is impossible to deduce how the principle could be thought in the first place. — Mww
You're saying there are truths that have no proof from experience and none a priori. Yep.It is already given no proof from experience is possible, in that the iterations of the statement are infinite. We have nothing with which to judge infinite conditions, except the logical validity of the principles by which the iterations stand as proven a posteriori, which is of course, the epitome of knowledge a priori. — Mww
You're saying it doesn't matter if maths is true, only that it is consistent. Perhaps.We don’t care if the conjecture is true, we can’t ever arrive at its finality anyway; we only care that the principles which ground the conjecture, work together and do not contradict themselves. We know a priori the principles of universality and absolute necessity, from which is given the LNC. From the LNC is given validity of the conjecture, even without the possibility of empirical proof for it. — Mww
I don't see how this works, nor how it follows from what went before. We know from Gödel that there are mathematical truths without proofs. What's puzzling Kripke is what it might mean to call such truths a priori.What it might be to claim it is true a priori, then, is just to show that if it isn’t, the entire base of human intelligence, re: logic, is junk, insofar as if we cannot use the LNC to validate the conjecture, the use of it to validate anything at all becomes questionable, which is itself a contradiction. — Mww
"Heat is necessarily the motion of molecules" cannot literally be true
— RussellA
I don't agree. — Banno
What will probably be argued by Mww is that, if heat is the movement of molecules, then while we learned this, it is an a priori fact deriving from the definition of heat. — Banno
we know stuff only by induction or by deduction? — Banno
What's puzzling Kripke is what it might mean to call such truths a priori. — Banno
Any empirical knowledge is contingent — Mww
The actual world is a possible world. The alternative would be to claim that the actual wold is impossible. — Banno
things known empirically that he claims are necessary truths. — Banno
….things known empirically that he claims are necessary truths. — Banno
he gives a variety of examples of what he says are necessary a posteriori facts... — Banno
But given that a posteriori we know that heat = the movement of molecules, then it's the same in every possible world. Or at least, that seems to be Kripke's argument...........I don't see how molecules could exist but not their movement — Banno
Well, Kripke isn't going to disagree with that. He says as much. so I don't see how it is a misunderstanding.Things that are known empirically is one thing; that there are necessary truths is quite another. — Mww
It cannot be an absolute necessary truth that H is P, — Mww
Well, no. Heat is measured in Joules. It is the flow of energy from place to place. I don't think we can finesse that away. — Banno
1) Heat is the transfer of thermal energy between two bodies, not the flow of thermal energy between two bodies. — RussellA
current principles of physics allow that the second body, the receiving body, is not necessary — Metaphysician Undercover
Radiation of heat from an object........heat can radiate — Metaphysician Undercover
The rest of your post seems to be a move from looking at the logic to demeaning the logician. — Banno
Heat doesn't radiate. Heat is the transfer of thermal energy between two bodies.
There are three modes of heat transfer, conduction, convection and radiation. The transfer of heat by radiation needs no material carrier. Thermal radiation is electromagnetic radiation.
It is incorrect to speak of the heat in a body, because heat is restricted to energy being transferred.
Kirchhoff's law of thermal radiation is regarding a body at temperature T radiating electromagnetic energy. The body is not radiating heat, it is radiating electromagnetic energy.
The sun doesn't radiate heat, it radiates thermal radiation. If this thermal radiation doesn't hit a second body, as heat is the transfer of thermal energy between two bodies, no heat will be transferred.
When Theodore Parker said "Cities have always been the fireplaces of civilization, whence light and heat radiated out into the dark", he was using it as a poetic metaphor. — RussellA
Well, no. Heat is measured in Joules. It is the flow of energy from place to place. — Banno
And there are a few eccentric posters on a pop forum who disagree with his account because it is at odds with other views they advocate. — Banno
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