Is logic valid?

Philosophy doesn't presuppose the validity of logic?

It usually does. However, it is also the only field (that I can think of) that would be willing to question that presupposition.

Which branch of philosophy (or philosopher) however unusual questions the presupposition that logic is valid?

None that I know of. It's not a very useful topic to discuss because it has no practical effect.

It would apply to everything. Theism, atheism, string theory, 2+2=4, etc.

It wasn't specific to my religion, but it would apply to it. However, it would apply equally to your atheism. That's why it has no practical effect, because it invalidates everything equally.

Simply because I wouldn't be certain that it is true doesn't mean that it isn't true.

It could still have a 99.999 percent chance of being true. Not certain just means not 100 percent.

I can use this exact same argument for my case. What makes yours more true?

Are you saying you know for sure God exists as in 100% or 99% sure or something else? 

It's a philosophical thought experiment meant to show how you can't be certain about anything because you can't be certain about logic.

I am simply showing the real life examples of philosophy. If we take this theory and apply it to the real world. We realize we can't be certain God exists.

Do you want me to speak to you in another thread?

Why single out God?

No, I don't have time for a "Does God exist?" debate right now.

Wouldn't you consider God to be one of the most important questions?

I consider it the most important question, but there are times when I want to talk about something else, like whether or not logic is valid. 

Logic is valid just not valid inherently like with pretty much anything in the world. It is the most valid thing we have in gaining information. 

I consider it the most important question, but there are times when I want to talk about something else, like whether or not logic is valid. 

I used this argument in a different forum and decided that it needs its own topic simply because it is so unusual and counter-intuitive.

There is no way to be certain that logic is valid. We can divide any possible argument into the two categories of logical and illogical. Since anything that is not logical is by definition illogical, and vice versa, these are the only two possible categories. My argument follows inevitably from these simple and indisputable premises.

P1: Every argument is either logical or illogical.

P2: Any attempt to use logic to prove that logic is valid is circular, because the use of logic presumes that logic is valid.

C1: It is impossible to use logic to prove that logic is valid.

P3: Any attempt to use illogic to prove that logic is valid is inherently contradictory.

C2: It is impossible to use illogic to prove the validity of logic.

C3: Because of P1, C1, and C2, there is no possible argument that can prove that logic is valid.

As a result, no matter how self-evident logic seems or how well it is supported by the evidence, we cannot prove that logic is valid because such arguments are logical and therefore circular. Since it is impossible to be certain that logic is valid, and since all knowledge is dependent on the validity of logic, it is impossible to be absolutely certain that knowledge is true. Consequently, knowledge cannot exist, since any knowledge would be based on the uncertain assumption that logic is valid.

So what do you think? I'm guessing we all agree that logic is valid, but do you think it's possible to prove that logic is valid? Is my reasoning correct, or does it have a flaw(s)?

In other words, can we prove logic is valid, or do we just have to assume that it's valid out of necessity?

It's just that I can't prove it's valid.

Yes, it applies everywhere.

 However, can you prove that it's self-evident or that it applies everywhere?

......even that assumes that the universe can be made sense of.

Proof is in the pudding i.e. the resultant you desire, arrives via your logic, then no worries.

Is there some aspect of Universe you dont understand? Even if you dont understand others do or may claim that they do.

Scientists claim there exist 1st law of thermodynamics because no evidence of other such conclusions exist to date.

I agree. It's just that I can't prove it's valid. Yes, it applies everywhere. Yes, it's self-evident. However, can you prove that it's self-evident or that it applies everywhere? We are forced to assume those things in order to make sense of the world, but even that assumes that the universe can be made sense of.

I'm not saying that logic isn't valid. It's just that we can't prove it, so we can't be 100% certain, just 99.999...% certain.