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1. Originally Posted by MacGuffin
I don't think "logic" is being defined correctly.

Logic based on false assumptions is still logical. Logic is just a tool.

Now, can logic result in irrational conclusions? Yes, indeed...
Yes that's formal logic, perhaps the most important definition.

It's been a bit corrupted since then. Which is a shame because it has simple answers for most questions, including this one.

If the conclusion follows the premises, it is logical, if not, it is illogical. So the truth value of the premises does not affect the logic. So, a logical conclusion can be a false one. Of course, if the premises are false, it doesn't mean the conclusion is false, just that there's no logic there. In fact, both the premises and the conclusion can be true, but there be no logic there, because the conclusion doesn't follow the premises.

So, in this sense, it's "illogical" to assume a logical conclusion is a true conclusion or that an illogical conclusion is a false one.

The corruption of logic's meaning is also awesome, because the English language is nice like that. There's good reason to think this aspect is one of the things which help with abstract thought, along with how fluid the syntax is. It's probably nice for poetry and things too.

Originally Posted by Chunes
Logic requires assumptions and careful boundaries to work properly.

If someone uses logic to arrive at a conclusion about say, Israel's motives behind its latest military bravado, then I can only assume his premise takes into account every factor in the universe, since every factor in the universe would be required to make an accurate observation.

Logical streams of cause and effect assume that only one thing causes the next thing to happen. Existence isn't like that.
That's where inductive reasoning steps in. That is, reasoning that does not arrive at a definite conclusion. Even certain "logical" fallacies sometimes become logical when using inductive reasoning (ad hominem, ad populem, appeal to authority etc.)

Bare in mind that probability, what inductive reasoning deals with, is merely a measure of the referee's knowledge.

Originally Posted by Chunes
Nor have I seen an example of logic used to prove anything outside a closed axiomatic system.
I assume you mean this but, that is because that's the only realm logic can prove (certainty) anything within.

Again, all that is with formal logic, there are many colloquial definitions of logic outside of this scope.

2. Originally Posted by ragashree
This

Any logical construct rests on the foundation of its premises. If these are not sound, the whole structure collapses or is unstable.

The easiest way to spot illogical logic is when it circles back around instead of proving or disproving either true or false. Basically for your last statement to be what you want it to be(true or false) you must change the begining which changes the whole reasoning altogether. The thing is that you can logically follow that path over and over and come to the same results. The only way to fix it is to modify the logic.

3. False assumptions such as... human emotion? Some might say "I am logical because I'm unaffected by emotions". These people are idiots, I know because I used to be one. Logic is a framework of cause and effect that we can recognize, but as soon as someone tries to be logical they are arent factoring in their inability to do so.

There is truth, and then there is everything else. Whether you know it or believe it doesn't make it go away. Why bother with so-called logic when there is something far greater?

4. when it contradicts common sense and facts.

5. Common sense could be wrong. Recorded facts could be based on faulty assumptions.

6. touche. i actually feel stupid seeing what i wrote now...but continuing on,

if that is known, and there are no reliable frameworks, references, or experiences, then "logic" cannot be applied.

7. Logic is never illogical. Logic can lead to illogical x, but you cannot say "Logic = Illogical" ever. Just like you can't say "1 = 2" .. It always has to be "1 + 1 = 2" that +1 being whatever.

Anyways, the closest answer I saw to even remotely convincing me was the post on the math theories.

8. Originally Posted by kyuuei
Logic is never illogical. Logic can lead to illogical x, but you cannot say "Logic = Illogical" ever. Just like you can't say "1 = 2" .. It always has to be "1 + 1 = 2" that +1 being whatever.

Anyways, the closest answer I saw to even remotely convincing me was the post on the math theories.
Logic is the study of reasoning. Logical will never be illogical. Illogical logic is when you are not really studying reasoning, but when you apply logic and put it up to be scrutinized. At that point it is either illogical or logical.

9. Seriously.....you are much better at being irrational than being logical. You are also good at acting logical, unfortunately you cannot escape your own master plan.

10. Logic: The study of the principles of reasoning, especially of the structure of propositions as distinguished from their content and of method and validity in deductive reasoning.

Logical: Reasoning or capable of reasoning in a clear and consistent manner.

Illogical: Contradicting or disregarding the principles of logic.

Deductive Reasoning
The most common method of building an argument is deductive reasoning, where a syllogism is constructed using a major premise, a minor premise and a conclusion. In most cases, the major premise is the all-encompassing, worldview idea, while the minor premise is the idea specific to a given argument. The conclusion then naturally follows from the two premises.

For example, in an essay arguing that handguns should be outlawed, the syllogism might look like this:

Major Premise: That which is potentially dangerous should be outlawed.
Minor Premise: Handguns are potentially dangerous.
Conclusion: Handguns should be outlawed.
When evaluating the merits of a deductive syllogism, the critical thinker needs to ask if an argument is sound. That is, are the premises true (do you agree?) and are the premises valid (do they relate to each other?). If the syllogism is either false or invalid, then the argument is unsound.
And no I have nothing against handguns as I did not write the above quote.

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