Can logic be used to prove any belief?

Question

I have witnessed a lot of debates and arguments of different beliefs, and noticed that each side uses logic to prove its point. So, can any belief be proven by logic regardless of its nature (religious\irreligious) and regardless of its differences (Islam\Christianity\Judaism etc.)?

Answer 1

According to the Duhem-Quine thesis and the underdetermination of theories in philosophy of science, no theory can ever be completely dismissed by empirical data (See Quine's "Two dogmas of empiricism" 1951).

I will give you two examples, one historical and one hypothetical, to illustrate my point:

• In 1845, Newton's theory of motion was contradicted by the measurements of the motion of the planet Uranus. Did this data mean that Newton was wrong and we should reject it? Or did it mean that we were missing information? As it turns out, in this case we were missing information. There was an unknown planet, later called Neptune, which was causing the orbit of Uranus to deviate from the orbit predicted by Newton's laws. Imagine in 1845, two scientists, one anti-Newton, the other pro-Newton: the first argues that the orbit of Uranus is definitive proof against Newton's laws of motion. The other one argues "Ahhh, but how do you know that there isn't another planet disturbing Uranus' orbit?"
• A scientifically inclined person and a Christian fundamentalist (who believes in a literal interpretation of the Bible) are arguing over the story of creation in the Bible: The secular person argues that the fossil record and geology disprove once and for all the Biblical account of creation. The religious person responds "Ahh, but how do you know that those fossils weren't put there by Satan to turn people away from God? How do you know Satan didn't plant evidence to make the world look like it was 5 billion years old, when in fact it was only 6000 years old?"

The point here is that any set of true facts about the world can always be reconciled with a given theory, as long as you are willing to include additional hypotheses and assumptions to bridge the theory with the fact. So to answer your question: Yes, logic can be used to prove any belief, as long as a person is willing to add additional assumptions to support their belief.

So then, how can one settle such arguments?

• You can try to show that a set of assumptions are contradictory, but then you run the risk of having the opposing party simply adding new assumptions which make the original contradiction disappear.
• More importantly, and this was Quine's answer to the dilemma, you can resort to pragmatism: We can never decide between different belief systems using logic, but of the competing belief systems, which one has proven the most useful? Which one has lead to the most good, improvement, etc....

Answer 2

The basic laws of logic are used in any reasoning. Implicitly, we are always using deduction strategies. Therefore, a proof of anything will use logic. However, that does not mean that a religious belief can be proven using logic alone.

In Christian theology, a distinction is made between general and special revelation. General revelation is 'the disclosure of a natural knowledge of God via the structures of creation'; special revelation 'the disclosure of a special knowledge of God via divine redemptive acts and words.' (Plantinga 2010)

There are some medieval philosophers like Anselm of Canterbury and Thomas Aquinas who have developed proof-like arguments for God's existence. They were already debatable at that time and especially Thomas' five ways aren't considered valuable as a proof any more. It does show that people have thought about proving things about the God-concept in a general revelation-manner. Also the God proof of Descartes can be seen from this perspective.

The 'general revelation proofs' for God's existence lead, even if they are correct, to a very restrained image of God. For example, Aquinas could only prove the existence of a first cause and Anselm only that of a perfect thing. Descartes only arrived at an entity that guarded his senses to not be fooled by an evil genius.

To actually arrive at the God of a religion from this takes some effort. That is why Thomas Aquinas cannot really be seen as a purely general revelationist. That is why:

According to Aquinas faith is a conviction as unshakeable as knowledge, but unlike knowledge it is not based on rational vision; it depends instead on the acceptance of something that presents itself as a revelation from God. The conclusions of faith cannot contradict those of philosophy, but they are neither derived from philosophical reasoning nor are they the necessary basis of philosophical argument. — (Kenny 2006, p. 153, emphasis mine)

There are also philosophers who argue for an approach strictly based on special revelation, most notably Karl Barth, who thinks the theologian should be focused on God talking (special revelation) rather than human chattering (general revelation) (Barth 1963, 280-97). This position is however difficult to uphold in Christianity considering many scripture passages pointing to general revelation (e.g. Ps. 8, Job 38:1-39:33).

And then there are philosophers who claim faith cannot be rationally justified at all, for example Kierkegaard:

First of all, we can never achieve complete certainty about historical events. But a mere judgement of probability is insufficient for a religious faith which is to be the basis of eternal happiness. Secondly, historical research is never definitively concluded, so if we are to use it as the basis of our religious commitment, we must perpetually postpone that commitment. Thirdly, faith must be a passionate devotion of oneself; but objective inquiry involves an attitude of detachment. We must therefore give up the search for certainty, embrace the risk, and take the 'leap' of faith. — (Kenny 2006, p. 329, emphasis mine)

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Summary

• Logic is always used in arguments, but logic alone doesn't seem to be enough to arrive at a proof for a non-abstract god's existence.
• There is a classical distinction between general and special revelation.
• Medieval philosophers have attempted to prove God's existence from general revelation alone, but it takes some special revelation to arrive at the Christian god (or any other non-abstract god).
• A strictly special revelation approach is difficult to uphold in Christianity.

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References:
_{Barth 1963: K. Barth. Church Dogmatics I.2. T. & T. Clark 1963.
Kenny 2006: A. Kenny. An Illustrated Brief History of Western Philosophy. Blackwell Publishing 2006.
Plantinga 2010: R. J. Plantinga, T. R. Thompson and M. D. Lundberg. An Introduction to Christian Theology. Cambridge University Press 2010.}

Answer 3

Logic is about the connection between propositions. It is not about the truth or lack thereof of proposition. In consequence, logic is about whether arguments - ie, concatenations of propositions - are valid, not about whether they are true.

So, logic can prove that an argument is valid, or invalid. Not that it is true or false, nor that the propositions used in the argument are false or true.

Here is a valid argument:

1. All the presidents of the United States are genocidal maniacs.
2. Barack Obama is the current president of the United States.
3. (from 1. and 2.) Ergo, Barack Obama is a genocidal maniac.

It is valid because, if its premises (1. and 2.) were true, then 3. logically follows. It's conclusion (3.) is false because one of its premises (1.) is false (or so we fervently hope).

Here is an invalid argument:

1. Salvia flowers are blue.
2. General Electrics' logo is blue.
3. (from 1. and 2.) Ergo, the sky is blue.

Note that all propositions, both premises (1. and 2.) and conclusion (3.) are true. But the argument is invalid, because the conclusion does not follow from the premises.

Here is another valid argument:

1. All burumbles are wentiful.
2. This garpic is a burumble.
3. (from 1. and 2.) Ergo, this garpic is wentiful.

Here, we don't even know whether any of these propositions is true. However, we know that if 1. is true, and if 2. is true, then 3. is necessarily true.

So, logic can only be used to demonstrate that an argument is internally consistent, ie, that its conclusion follows from its premises. It cannot prove wheter the argument is consistent with the observable universe, ie, that its conclusion is true, unless we are perfectly certain that all the premises are true (which usually is only the case for quite trivial arguments).

Answer 4

Yes. Logic is only as reliable as it's starting point. Every logical proposition is based up one or more premises. Depending on the reliability of these premises, logical processes can be used to 'prove' just about anything.

For instance, let us pretend that I wish to prove that the universe is secretly controlled by bees.

This would be difficult to logically prove only upon observable data. However, when I present a book titled "Everything within these pages is 100% true," (which happens to include a chapter on "How the bees control everything!"), it becomes trivial to logically prove my position. Based on the premise that my book is correct (I mean come on, look at the title), then it logically follows that bees do indeed control everything. And, as you may well know, the universe is included in "everything" so obviously we are already subject to the iron-mandibled rule of our busily buzzing overlords. And we didn't even know!

Answer 5

I suppose it depends on what you mean by logic. However, one thing you might be interested in knowing is that even in mathematics--perhaps one of the most pure applications of logic--there are some questions that cannot be decided by logic alone. Loosely speaking, Gödel's incompleteness theorems show that, for the natural numbers (positive integers), there are statements that are true but unprovable in any logical system that is internally consistent (none of the axioms violate each other) and also does not have so many axioms that no computer program could list them.

These incompleteness theorems would seem to be a counterexample to the proposition that all beliefs can be proven or disproven by logic, and thus answer your general question (no, all beliefs cannot be proven or disproven).

Regarding religious questions specifically: Gödel's theorems don't apply, but I would think that there likely exists some sort of analogous situation. Religious beliefs by their very nature are based on faith--and if we can't even prove or disprove all statements in mathematics, how should we expect to do so for religious statements?

Answer 6

I think you may be confused between "rationality" and "logic"

If you are thinking that "logic" is the use of reasoning then Yes. Using our reason we can prove truth and also vice versa. Humans even lie to themselves, with a reason...

Answer 7

• Consider logic as a machine taking inputs and yielding outputs.

• If the input is false, the output may be true or false.

• But if the input is true, the output is 100% true .

• This is because the logical machine is designed to be " truth preserving".

Note : Saying that logic is "truth-preserving" is just another way to state that " a reasoning is valid deductively just in case , if the premises are true, the conclusion must be true".

• So yes , logic can prove beliefs, provided the data that are used as inputs are true.

Answer 8

Can logic be used to prove any belief?

It depends what you mean by "prove."

Two different concepts in logical argumentation are soundness and validity. To better explain soundness and validity, I will use an analogy:

In January of 2004, mars rovers “spirit” and “opportunity” landed on mars. 8 years later, another rover, “Curiosity,” landed. Curiosity was equipped various instruments for collecting data:

• Video cameras for capturing photographs

• A Rock Abrasion Tool (RAT). The outside of a boulder, exposed to martian air, is chemically different from the inside of the rock; like a candy wrapper surrounding a candy. The RAT was able to create holes 45 mm (about 2") in diameter and 5 mm (1/5") deep in the rock so that the inside could be studied.

  • An Alpha-Particle X-Ray Spectrometer (APXS) was able to determine what elements are in the rock and in what proportion.

  • the Mössbauer Spectrometer gives off gamma rays and uses the energies of the returning gamma rays to determine the composition and abundance of iron-bearing minerals in the surface rocks.

    1. The robot has video cameras and other sensors for collecting data.
    2. The robot also has a computer for processing data, but the computer can collect no data directly.

Logic can be thought of as "what can a mars rover do if you turn off its video-cameras, spectrometers, and other data collectors." Logic is closely related to the study of what a computer can compute. Logic is also the study of how to take some information as input, and output new information.

For example, Bob is allowed a 30 minute break at the middle of his work shift. He wants to know what the clock will say when it's time to go back to work.

• INPUT 1.... break begins at 8:20PM
• INPUT 2 .... break is 30 minutes long
• OUTPUT ...... break will end at 8:50PM

If humans turn off their metaphorical sensors (ears, eyes, sense of touch, etc...), then humans can still make new inferences. This is because old data can be recombined to give us new data. Bob did not initially know that break time ended at 8:50PM. Although the calculation is easy to make, it still takes computational effort. to add 30 minutes to 8:20PM. Although it may happen in a fraction of a fraction of a second, even an electronic man-made computer still requires a modicum of time to compute 2+3.

• loosely speaking an argument is sound if the data collected by the video-cameras, microphones, tactile sensors, etc... was correct.
• an argument valid if we pretend the input data is correct, and use high quality reasoning to infer new facts from old facts.

Let us look at an example of a valid, unsound argument. In the year 2018, Emily Levine gave a TED talk titled, "How I made friends with reality." Ms. Levine made the following argument:

1. For any person, if that person is afraid of death, then that person is anti-woman (axiom)
2. I am a person (axiom)
3. If I am afraid of death, then I am anti-woman (from lines 1 & 2)
4. If I am anti-woman, then I am not a feminist (axiom)
5. I am a feminist (axiom)
6. Therefore, I am not afraid of death (output/result)

Although Emily Levine's argument is ridiculous, it is 100% valid. The argument is valid, but unsound. If the inputs were correct, then the output would be correct. However, the inputs are wrong. Notably, the input that afraid of death does not make a person "anti-woman."

Part of the original Emily Levine is as follows,

"my real problem with the mindset that is so out to defeat death is if you're anti-death, which to me translates as anti-life, which to me translates as anti-nature, it also translates to me as anti-woman, because women have long been identified with nature."

It is true that women have long been identified with nature. However, the rest of that stuff is nonsense. In the past, there have existed women, some of whom were ardent feminists (very pro-woman), who did not want to die, but got old, got sick, and died anyway.

The following are two definitions of "proof:"

1. proof(1)...... an argument is a proof if it is logically valid and logically sound.
2. proof(2)...... an argument is a proof if that argument is logically valid. The argument may or may not be logically sound.

Can logic be used to prove any belief?

logic can be used to type-2 prove any belief. That is, for any belief B there exists a 100% valid logical proof that B is true.

PROOF: Without loss of generality, take belief B be "all horses have wings, eat rainbows, and live in Australia."

1. If at least one person on planet earth ate a hot dog before the year 2020 then all horses have wings, eat rainbows, and live in Australia
2. least one person on planet earth ate a hot dog before the year 2020
3. From line 1, line 2, and modus ponens, all horses have wings, eat rainbows, and live in Australia.

The above was a completely valid proof that all horses have wings, eat rainbows, and live in Australia. The proof was unsound.

However, logic cannot be used to type-1 prove any belief. That is, there exist beliefs B such that every valid proof of B is unsound.

To correctly answer a question like, "Can logic be used to prove any belief?" you must first decide what it means to "prove" something.

The statement "logic can be used to prove any belief" contains a grain of truth if you are looking for logical validity only, and you ignore soundness.

Logic is like a coffee grinder. You put coffee beans into the machine and coffee grounds come out. For the logic machine, you put feed data in, and new data comes out. Logic does not care where the input facts came from, or whether those input facts are correct or not. You could put corn in the coffee grinder, and maybe the output would be ground corn. Garbage-in, garbage out.

Answer 9

Another strange example of something being both empirical and a priori would be the existence of time itself.

Human Beings, perhaps not very well and strongly, do indeed have an "internal clock" built-in. The observer can tell that time has passed very roughly, even when deprived of the traditional senses.

At the same time, if you leave an apple on your desk and come back in six-weeks, the apple will have decayed. The change in the apple's visual structure is circumstantial evidence of time.

We have essentially have bridged both claims of [1] axiomatic-claims / tautological-claims and [2] claims based in empirical evidence.

• (https://plato.stanford.edu/entries/kant-spacetime/)
• (https://en.wikipedia.org/wiki/Spacetime)

Answer 10

No, it cannot. Logic itself can "rationalize" any belief. But "proof," in any scientific or juridical sense, entails empirical evidence to support the reasoning.

A great deal in the evolution of philosophy addressed this very issue. The Platonic dialogues concern the evils of specious reasoning by the Sophists and Rhetoricians, who taught how to "prove" both sides of any issue, an art still studied by lawyers and politicians.

The purely rational arguments of the Scholastics, while advancing logic, led to a general revolt by philosophers against such "hair splitting" and "angels on pins counting," producing Bacon, Galileo, and the scientific turn.

Reasoning can rationalize both sides of any issue; logic can tell you if the reasoning is correct; but in the modern sense only induction supported by evidence (to grossly simplify) can prove conditionally that a synthetic belief is correct.

Since the rise of scientific method, and in fact even before, philosophy has generally withdrawn from "undecidable" beliefs that do not entail testable evidence. Since these constitute the vast majority of our beliefs, what we believe remains prey to rhetoric, passion, demagoguery, habit, faith, and quackery, the human world in which the power of logic is feeble.