My response to: "If it was impossible to prove god did not exist then he must be assumed to exist." is fairly simple.
Prove it is impossible to prove god does not exist.

 I take the opening claim that if one can not prove that god does not exist, therefore god exists (or should be assumed to exist) by the law of non-contradiction, to be obvious rubbish. That law makes no such proposition, only that something either exists or does not. Asserting either claim then requires evidence, without which certainty you have no certainty but can still operate on the basis that absence of evidence is currently sufficient evidence of absence.

If being unable to prove something does not exist means it exists, then I will leave you a few seconds to make up any ridiculous proposition you please and thereby be able to say it exists, solely by virtue of its non-falisifiability.

Invite your brother to prove there is not a penguin which dines out on biblical gods, which regrow overnight like Prometheus' liver, so the penguins can have breakfast too.

There is no reason to assume something not relevant and without evidence.

I agree completely, Pacioli.

This is a more humorous version of Bertrand Russell's teapot argument which it appears that your brother is using. No one can prove the absolute non-existence of the almighty teapot, however there is no evidence to support that there is any such orbital teapot.

The link is a brief description of the argument if you haven't read it already.

en.wikipedia.org/wiki/Russell%27s_teapot

Conversations with your brother have got to be extremely frustrating. My husband's brother is a vicar, so I can sympathize. Perhaps a small video suggestion.

Youtube search Tim Minchin's animated movie "Storm". I watch it when I need a giggle after dealing with overly philosophical poo-flingers. Enjoy!

No.

There's no 'need' to assume anything, nor is there any obligation to assume anything.

Assuming that something is true when you don't know, can get you dead, so, it's a patently stupid philosophy.

Taken to it's logical conclusion, the Christian must assume that Jesus is deader than a doornail.

In application, that is about as useless as a dimensionless number.

Any knowledge we can acquire is probable? Probable as in 'probably right', or probable as in 'probably wrong'?

Fallacy of equivocation.

What a bunch of vacuous word salad bullshit.

Because it can be wrong. And it's 'probable' that it is wrong, especially when it's fucking non detectable.

No, we can do more than that.

We can not worry about it.

"Que sera, sera"

It's really disturbing that these navel gazers argue in such stupid fashion with such a serious and straight face.

Essentially, the argument for 'god' boils down to this assertion that an eternal 'supernatural' always existed, because the 'natural' could not have always existed.

Oh, and this 'supernatural' is a stream of 'conscious thinking'. And these 'thoughts' form 'solid' matter which get injected with 'conscious thoughts' that are independent of the 'Big Kahuna thought' that bosses and threatens the other 'thoughts' that are temporarily combined with 'solid' matter.

What is also unequivocally asserted, (with absolutely no reasoning whatsoever) is that there can only be 1 'Big Kahuna Thought'.

IOW, no other equally 'Big Kahuna Thoughts' that could conflict, exist.

It's funny the double standard of ruling out probabilities these 'rigorous thinkers' employ.

It's an absurd line of 'reasoning'. What a bunch of horseshit...

No. He has it backwards.

It is the assumption that only knowledge that is 100% certain can count as knowledge that has the problems.

There are statements that we can know with 100% certainty are true, such as "any premise that involves a contradiction is false".

Or "some statements can be shown to be false". And so on.

But many statements, such as absolute assertions that specific entities exist, as long as their existence does not entail clear contradictions, would require perfect and complete knowledge of reality to 'know' if they are true.

Most of the imagined 'problems' of holding knowledge with some degree of uncertainty attached are due to trying to fit it into arguments constructed with simple binary logic, where there is only 'true' and 'false'.

What is now referred to as Bayesian analysis puts the handling of uncertainty on a firm mathematical footing, and allows us to estimate the degree of confidence we can have in any conclusion based on the estimated probability of each of the assumptions and observations being true.

This is exactly what I think - trouble is it's hard to maintain composure in the face of arguments that endeavour to completely remove the basis of your reasoning. If there's a possible god then there logically must be a god and if you deny this you are denying the law of non contradiction. If your response is that there's no evidence of god in this universe or we can never know with certainty if there is a god outside this space time, nor anything absolute at all about things outside our universe then you run foul of the biggest fucking irritation of all. The most ironic words a christian man can utter. The words "prove it". 

We've encountered these arguments for years and years from typical presuppositionalists.

Boil down their arguments, and they are pretty ridiculously obviously just plain old naked assertions.

The 'problem' with presuppers is that they taken an extra step to lock down their delusions into their heads: They presuppose that they are right, and cannot possibly be wrong, and so they no longer apply any skepticism to their underlying crazy assumptions. Instead, they project their own stupid epistemology onto everyone else, and then go on the 'offensive', claiming that nobody else can 'account' for this or 'account' for that.

It is blatantly obvious to any skeptic on the outside, looking in to the world of the presupper, that the presupper is the one who hasn't bothered to actually 'account' for anything. Scratch the surface just a little bit, and you'll find it's an enormous pile of steaming shi--fallacies of various types: God of the gaps (their 'account' is a big, smelly "GODDIDIT!!!!" ), reification (logic is 'absolute', 'universal', 'immaterial', and exists independent of our minds), psychological projection, argument from incredulity, etc.

As I said, though, they immediately go on the offensive, and so if you're unfamiliar with their tactics, you might find yourself trying to defend your modest beliefs against seemingly insane accusations.

The key is to keep bringing it back to their bald assertions. Which is damn easy, because nearly all of them I've encountered (I have no knowledge of your brother, obviously, so I'm not referring to him) are completely clueless when it comes to actual logic. Which is a damn ironic thing, since they seem to worship 'logic' as their god. It's just not the same 'logic' as the one that is used to operate your computer or to make progress via the scientific method, or to prove a theorem in mathematics, or to guide a rational discussion. Their 'logic' is a twisted concept, derived from their primary belief in a god, and seemingly founded on an axiomatic contradiction. Which is about the stupidest thing .... gah. I could rant all day.

Long story short: If you have to 'account' for logic, then so do they, by their own standards. Stick to a skeptical stance. Don't bother to try to defend logic if you don't feel confident to do so. You are not the one making the claims here. They are. Burden of proof. It is on the one who makes the claim. They claim god exists. Challenge them on that, and keep hammering on them with basic, basic questions, like "But how do you really know that?" Ultimately, they have no answer to that. It comes down to 'faith' in the end, as it always does. They are on no better ground than any theist.

What logic really is:

A cultural invention of humans, like mathematics, developed and refined over thousands of years, starting primarily with the ancient Greeks (such as Aristotle), from whom the word 'logos' comes. 'Logos' originally meant simply 'word', but began to take on a more sophisticated meaning (along the lines of 'understanding', or 'reason'), and later got picked up by mystics (who meant something like 'universal order') and eventually Christians. Jesus is supposedly 'the Word', literally, 'Logos'. I suspect this is where the connection lies in their worship of 'logic'.

Today, the word logic has several related meanings such as 'structured thought', 'disciplined study' (e.g. biology), and 'line of reasoning'.

However, in most discussions such as this, we are talking about the modern study and application of logic itself, as embodied in the accumulated theories and systems of logic such as symbolic logic (used by mathematicians, scientists, and modern philosophers to prove theorems), Boolean/von Neumann logic (runs your computer), and various alternative systems such as modal logic, quantum logic, etc. Some are more useful than others (hint, hint).

Logic, as it is known and used today, is definitely a cultural thing. You can get a book on logic (there are free (really free) pdf textbooks all over the place, some are excellent), and learn it on your spare time, or take an introductory course at a college or university. If you ever try to program a computer, you will need to learn at least some basic logic (to make sure the program works properly), which is actually easier than it sounds. There are different systems of logic, and we know who invented which ones, etc., so when a presupper tries to argue that logic is 'universal' and 'absolute', they are simply, frankly full of shi--making a bald assertion based on nothing but dogma.

What presuppers wish logic really was:

God, or some shi--

Universal, absolute, 100% reliable, unquestionable certainty. Independent of anything of this 'fallen world'. A massive baby blanket to protect them from fear of the unknown.

They are fundamentally insecure in their beliefs, believing that only 100% absolute certainty is worthy of any consideration as 'truth', even though no one has ever had 100% absolutely certain knowledge about anything. So, believing that only logic can supply such certainty, they frantically try to scrabble it up and horde it for themselves.

But they have no real understanding of actual logic, and so ironically they divorce themselves from the one tool that could help them overcome their irrational fear of the unknown. The 'logic' they want is not the real logic we have. Their 'logic' is as imaginary as Jesus or Yahweh. It's more akin to the Holy Spirit or something. It's the 'Logos' of the mystics, the 'universal order of things', as distinct from pure 'Chaos', the terrifying and unpredictable unknown.

Back to reality:

Logic itself is not empirical, like math is not empirical. However, neither logic nor math would be much good if they didn't reflect our understanding of the universe. And so, while they are not empirical themselves, we have, over the centuries and millennia, whittled down our systems of numbers and arguments so that they have become extremely useful tools of thought. And as tools of thought, they form the basis of modern science, which is eminently empirical in nature.

You could, in principle, develop a system of logic that is completely useless. I'm sure many such systems have been invented by crazy people over the years. But where would you go with a useless system of logic? Nowhere. Exactly. (These go to eleven.)

If your 'logic' leads you to stupidity, then the only way it will ever make it in the world is if it is some kind of crazy dogma (like religion).

Other than that, we have seen systems of logic come and go through the ages. While they are not empirical themselves, per se, our empirical understanding of reality will cause us to discard the useless logics and keep the useful ones. Logic reflects the order of the universe, it is not itself the order of the universe. Although, that is what the presuppers try to argue, and where they go catastrophically wrong. They confuse the map for the territory. And in the process they divorce themselves from reality. It's quite tragic, actually.

The 'law of non-contradiction' is not an absolute, universal 'law' of the universe, 'given' by a 'law giver'. It is a statement about our understanding of the universe. It is a feature of the map, not of the territory. It is like saying that North is a 'universal', 'absolute', 'immaterial', 'transcendent', 'whateverthefuck' thing that comes from 'god', and that we 'presuppose', and that atheists cannot 'account' for.

It's just fucking North, dude. We call it that because it is useful to call it that, and it helps to organize our thoughts and communication in regards to direction and orientation. 'North' is a human concept, invented by humans. It reflects reality, because in reality the Earth spins on its axis and this gives a natural 'order' to our terrestrial sense of direction, but 'North' is not that natural order itself.

To promote a human concept into a mystical realm of imagined existence is a tremendously hideous fallacy known as reification.

'North' exists, but it doesn't exist outside of human culture. It exists as a concept, whether written on a map, or defined in a dictionary, or learned in a brain, or programmed into a GPS system. These are all physical systems. Presuppers talk about 'immaterial', but have no understanding of the difference between naive materialism (which nobody on the planet actually believes in) and modern scientific physicalism.

Logic is in the same general physical category as 'North'. It is conceptual, cultural, and--at its basis--informational. It consists of systems and structures and relationships between them, as well as processes (such as thinking and communicating) which are purely physical, and can be 'accounted for' by physics (specifically, information theory). There is no magic to it. No supernatural, woo woo crap at all. And if the presuppers could make that realization, they would find themselves finally waking up to reality and throwing off their shackles of fear of the unknown.

Unfortunately, most of them are severely entrenched, and so divorced from actual logic that they cannot think themselves out of their own mental boxes.

Yep. That's basically it.

It's a bit hard to put the problem into words, but I guess it was today that 'reification' popped up in my head again. I had forgotten it, and talking with Tom the Who and wakawaka was like having the word on the tip of my tongue. It's really a fitting way to talk about the key flaw in their reasoning. I'll have to keep it in mind so I don't forget it again.

As for learning logic, I think it would be fun to do a few posts/discussions/whatever about core, basic logical principles and how to solve various logic problems/puzzles/questions. I've been thinking about it for a while now. Most logic texts are just too arcane and gratingly drrryyyyyyy yy y y <croak, cough>.

For a while I've been introducing logic to some of my students and trying to work out simplified explanations and analogies to make it more intuitive.

Here's my basic idea: Symbolic logic is no more complicated than the addition, subtraction, multiplication, and long division that kids as young as 8 can learn with no problem. I would wager that kids the same age could learn symbolic logic also, if it was taught with the same kind of gradual, step-by-step process that we use to teach from basic counting up to complex long-division.

I'm not there yet, but I'm constantly working on it. The problem of 'how to teach logic' is itself an interesting problem for me to think about and experiment with.

So, if you want to try, we could try to work through some problems from your logic books or something. Could be fun. Whaddaya think?

Their 'argument' (TAG) is circular, and it's patently stupid and self refuting, if you think about it.

WTF are these 'logicians' deciphering?

Reality.

You cannot know if your 'thoughts' are compatible with reality, unless your thoughts are compatible with reality.

How do you reach a firm conclusion when you haven't really firmly concluded it by testing it for compatibility with reality??

You can't.

Thought experiments are nothing more than thought experiments.

Saying 'Look! It works on paper isn't proof that it 'works' in reality.

Sorry, Chump.

They're being intellectually dishonest.

You cannot 'get ahead of yourself'.

Ask anyone who has studied fluid dynamics (previously called aerodynamics) how completely unpredictable it was/is.

These navel gazing philosophers will attempt to crucify anyone who attempts to 'pull yourself up by your bootstraps', meanwhile, it's their 'Stock and Trade'.

They'll obfuscate, not elucidate.

Ironic innit?

The moment these philosophers and logicians say something about 'everything'....it's a fallacy.

The pathetic prick sock puppet who's trolling this forum has even gone so far as to assert that 'foresight' is better at 20/20 vision than 'hindsight'.

You can't have a rational discussion with someone that delusional and dishonest.

It's very difficult to precisely articulate with the english language the linguistic trickery and fallacies of equivocations they resort to, to paint these 'immaterial' pictures.

Fluids go from high pressure to low pressure.

To type that fluids go from high pressure to low pressure is 'logical'; is not really increasing anything but the number of characters you've typed.

Fluids go from high pressure to low pressure.

Period.

Stop.

Fluids don't behave this way because it's 'logical'. Fluids behave this way because of the universal constants.

If the universal constants weren't universal, or constant, things would be completely 'unpredictable', and therefore behave in ways that we couldn't make sense of. When something does not follow a pattern that we can predict, it is unpredictable, and without 'reason', or 'senseless'.

Without 'sense', or 'reason' is 'illogical'. You can also extend 'sense' and 'reason' to 'purpose'.

Is it intellectually honest to claim that the behavior of water has 'sense', or 'reason' or has a 'purpose' to go from high pressure to low pressure?

It appears there's a 'pattern' to how particles and forces that we have detected, behave, because of the constraints and limits that exist. It appears that the particles and forces we've detected behave in a very strict fashion.

The patterns we consistently see be consistent, that enable us to make certain predictions that enable us to arrive at firm conclusions of the detectable portions of our universe, are the underpinnings of an understanding we term as 'logic'.

Our 'logic' (understanding) is confirmed by a posteriori testing with compatibility of reality, not by testing our 'thoughts'.

Several generations ago, it was completely logical to conclude that 'What goes up, must come down', because there was no knowledge to indicate otherwise.

Agreeing with your thoughts, that your mere thoughts are compatible with reality, is the definition of circular reasoning.

That's why you don't see any 'want ads' for philosophers...