My preferred approach is to use an analogous definition of truth as adequacy to the needs of a particular discourse. Then, for example, Newtonian physics is true with respect to many engineering needs. — Dfpolis
Concerning the
coherence theory of truth, I agree with Bertrand Russell's objections:
Perhaps the best-known objection to a coherence theory of truth is Bertrand Russell's. He maintained that since both a belief and its negation will, individually, cohere with at least one set of beliefs, this means that contradictory beliefs can be shown to be true according to coherence theory, and therefore that the theory cannot work. However, what most coherence theorists are concerned with is not all possible beliefs, but the set of beliefs that people actually hold. The main problem for a coherence theory of truth, then, is how to specify just this particular set, given that the truth of which beliefs are actually held can only be determined by means of coherence.
Therefore, I cannot agree with "Newtonian physics is true with respect to".
Recall that the root meaning of "geometry" is "land measure" and many of its axioms are true of real-world geometric relations. — Dfpolis
You would have to visit all possible planets in the universe in order to verify that they are true of real-world geometric relations. You cannot do that. You will only sample some of these. Therefore, you cannot exclude the existence of counterexamples. Hence, these axioms are neither provable nor true about the universe.
We also know some of the principles of real-world existence. No real thing can be and not be in one and the same way at one and the same time, and so on. — Dfpolis
Entanglement allows for simultaneous being and not being in the real world.
Schrödinger's cat is another example. Therefore, nuclear physicists seem to beg to disagree with you.
We can measure the interior angles of plane triangles and see if the results agree with the prediction that they will sum to two right angles. Then, the result is both axiomatically derived and experimentally confirmed. — Dfpolis
You cannot visit all possible such angles in the real, physical world. Therefore, the theorem is not provable about the real, physical world. It is only provable in the abstract, Platonic world in which the provability of this theorem is the result of the construction logic of that abstract, Platonic world. You can perfectly-well visit all such angles in an abstract, Platonic world. That doesn't cost energy. In the real, physical world, you would need more energy that you could ever practically amass.
I hate to break it to you, but there is no Platonic world. There is the real world and there are mental constructs that exist in the minds of people living in the real world. — Dfpolis
These mental constructs are abstract, Platonic worlds. They are not real. They are called Platonic because they are very similar to Plato's forms (but not necessarily the same):
Mathematical Platonism is the form of realism that suggests that mathematical entities are abstract, have no spatiotemporal or causal properties, and are eternal and unchanging. The term Platonism is used because such a view is seen to parallel Plato's Theory of Forms and a "World of Ideas" (Greek: eidos (εἶδος)) described in Plato's allegory of the cave: the everyday world can only imperfectly approximate an unchanging, ultimate reality.
A major question considered in mathematical Platonism is: Precisely where and how do the mathematical entities exist, and how do we know about them? Is there a world, completely separate from our physical one, that is occupied by the mathematical entities? How can we gain access to this separate world and discover truths about the entities? One proposed answer is the Ultimate Ensemble, a theory that postulates that all structures that exist mathematically also exist physically in their own universe.
Platonism is the dominant philosophical view in mathematics.
Historically, most axioms have been abstracted from our experience of reality. — Dfpolis
Originally, yes.
Abstraction in mathematics is the process of extracting the underlying essence of a mathematical concept, removing any dependence on real world objects with which it might originally have been connected, and generalizing it so that it has wider applications or matching among other abstract descriptions of equivalent phenomena.[1][2][3] Two of the most highly abstract areas of modern mathematics are category theory and model theory.
However, this is no longer the dominant source of inspiration for axiomatization.
For example, the
lambda calculus has absolutely no origins in the real, physical world. Nor do the various
combinator calculi. None of Stephen Kleene's work, such as
his famous closure, have any origin in the real world.
The entire discipline of
computability has no connection, and has never had any connection, with the real, physical world. There is absolutely nothing that looks like a
shift-reduce parser in the real world.
The mathematical foundations of computer science have never been about mimicking the real, physical world. That would simply be an exercise in futility. A running process on a computer system creates a virtual world of which the nature is studied using Platonic abstractions. Suggesting that these virtual worlds have originally been abstracted away from the real, physical world, is absurd. They do not exist in the real, physical world.
Alan Turing's Halting problem is provable in the abstract, Platonic world of running processes. What is the link with the real, physical world? In what way does the real, physical world contain running processes? Where are the naturally-occurring CPUs and computer systems?
Seriously, mathematics transcends the real, physical world. Physicists are just one group of its users. I do not understand why they think that they would be so privileged in connection with mathematics? Historically, there used to be an empirical link, but that link has been abstracted away a long time ago. There is no 20th century mathematics that still has such link. Mathematicians do not desire such link, because it would hold things back. Such link is very, very retrograde. Ever since the axiomatization of set theory in 1905 by Zermelo and Fränckel, absolutely nobody still wants that link.
Those of us trained in the natural sciences do not see unfalsifiable as an advantage, especially given that Godel work ruling out consistency proofs in systems representable in arithmetic. — Dfpolis
Well, ... in systems of which the associated language is capable of expressing the axioms of arithmetic.
Gödel was talking about the minimum power of a virtual machine and what we would today call its bytecode instructions. If the bytecode language can express Dedekind-Peano, the language can express (logical) truths that are not provable in the system.
Gödel's incompleteness is a language problem. The language required to express the axioms is more powerful than strictly what the axioms express. It is this fundamental mismatch that causes the problem.
In fact,
Tarski's undefinability theorem is much better at expressing what Gödel's conundrum entails:
Smullyan (1991, 2001) has argued forcefully that Tarski's undefinability theorem deserves much of the attention garnered by Gödel's incompleteness theorems. That the latter theorems have much to say about all of mathematics and more controversially, about a range of philosophical issues (e.g., Lucas 1961) is less than evident. Tarski's theorem, on the other hand, is not directly about mathematics but about the inherent limitations of any formal language sufficiently expressive to be of real interest. Such languages are necessarily capable of enough self-reference for the diagonal lemma to apply to them. The broader philosophical import of Tarski's theorem is more strikingly evident.
As a passing note, the axiomatic method does not work for morality, nor did Aristotle claim that it did. — Dfpolis
It does work for morality. According to Kant's Critique of Practical Reason, the core of a moral system are its categorical imperatives, i.e. its axioms. In fact,
Socrates already suggested that: "The understanding of mathematics is necessary for a sound grasp of ethics."
If they cannot be tested, they are unfalsifiable hypotheses and highly suspect. — Dfpolis
That is the empirical view in science, but a constructivist heresy in mathematics:
In the philosophy of mathematics, constructivism asserts that it is necessary to find (or "construct") a mathematical object to prove that it exists. Even though most mathematicians do not accept the constructivist's thesis that only mathematics done based on constructive methods is sound, constructive methods are increasingly of interest on non-ideological grounds.
If your only tool is a hammer, then the entire world will end up looking like a nail. If you cannot transcend the sandbox of physics, you will misunderstand and mismanage everything you ever do, outside physics. Is it so unthinkable to you that other epistemic methods are different from your own? Doing mathematics in the way you suggest, is simply not mathematics. It would be a failed form of physics.
As we have just agreed, the original justification of mathematical axioms was not via deduction from more fundamental assumptions, but via abstraction from reality. — Dfpolis
Only pre-20th century mathematics mostly originated via abstraction from reality. However, most of the progress that has been booked after that, does not.
Why do we care? Because mathematics is a science -- as one organized body of knowledge among many. So, we want its conclusions to be true. In fact, truth is a central issue in Goedel's work. The problem he exposed (which completely undercuts your position) is that there are true theorems that cannot be proven from fixed axiom sets. If mathematics did not deal with truth, this could not be the case. — Dfpolis
Gödel does not talk about correspondence-theory "true". You can even trivially understand that from his canonical example:
S = "S is not provable in theory T"
Is S provable in T? No, because that would be a contradiction. Hence, S is (logically) true. Therefore, we are now sitting on a theorem that is (logically)
true but not provable.
The language L associated with T is powerful enough to express S, and therefore, S is a relevant theorem in T.
The undefinability theorem does not prevent truth in one theory from being defined in a stronger theory. For example, the set of (codes for) formulas of first-order Peano arithmetic that are true in N is definable by a formula in second order arithmetic. Similarly, the set of true formulas of the standard model of second order arithmetic (or n-th order arithmetic for any n) can be defined by a formula in first-order ZFC.
In other words, it will be "true" and not provable in T, but it will be provable in any theory of which T is a sub-theory. The real, physical world is not chained into this tower of theories. Hence, it has nothing to do with correspondence-theory "true".
Further, if the truth of P is indeterminate, so is the truth of Q if its sole justification is P => Q. — Dfpolis
Yes, mathematical theorems are not correspondence-theory "true". They are only provable in their abstract, Platonic world.
So, the axiomatic method does not, and cannot, provide us with an exhaustive inventory of mathematical truths. That means that it cannot be the foundation of mathematical truth as you seem to imply. — Dfpolis
There are no mathematical truths. There are only theorems provable from the construction logic of their abstract, Platonic world, i.e. their axioms.
On your account, mathematics is no more that a game -- not any different from Dungeons and Dragons, which also has rules that are neither true nor false, but simply to be followed by those playing the game. — Dfpolis
Agreed.
Funding mathematical research would be a scam in which we are paying people to play arbitrary games, with no hope of advancing our knowledge of reality, however theoretical. — Dfpolis
There is no hope of advancing our knowledge of reality through mathematics. In relation to theories about the real, physical world, mathematics only supplies a consistency-maintaining bureaucracy of formalisms. Physics uses these formalisms. Hence, mathematics is useful to physics.
Finally, it mathematics were not true, it would not be applicable to reality. — Dfpolis
Mathematics is not applicable to reality. You will have to use another discipline for that purpose. You may indeed encounter mathematics as a tool to maintain consistency in what this other discipline claims, but that does not mean that mathematics would say anything about the real world.
Physicists who included mathematical premises in their reasoning, would be relying on claims of questionable or indeterminate truth, making their own conclusions and hypothetical predictions worthless — Dfpolis
Physicists do not include mathematical premises in their reasoning. They only maintain consistency in their theories by using mathematics. That works like a charm.