Irrational vs Illogical

ChosenByPasta
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Irrational vs Illogical

I've always wondered if there is an important distinction between these two terms. Are they used to describe different things? Or are they basically the same terms?
Just curious.

"Every true faith is infallible -- It performs what the believing person hopes to find in it. But it does not offer the least support for the establishing of an objective truth. Here the ways of men divide. If you want to achieve peace of mind and happiness, have faith. If you want to be a disciple of truth, then search." - Nietzsche


MarthaSplatterhead (not verified)
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I will take a stab at it. 

I will take a stab at it. 

Irrational pertains to basing something on a presuppostion.  Like saying god created us is irrational because there's no proof.  In a courtroom, you cannot build a case on circumstantial evidence.  That would be irrational.

Illogical claims just makes no sense at all.  Like 1+1=5.  

How'd I do? 


Apostate
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Logical and Rational, and

Logical and Rational, and Illogical and Irrational are adjectives. For definitions, it would probably be best to look at their corresponding nouns.

Logic is a method, the use of syllogistic reasoning. Rational comes from the Latin, the source noun is ratio. Ratio is normally translated as reason in English. To call something rational is to connote that it is reasonable. Generally it means that it is the result of thought, something deliberate, the product of judgement.

Something that is illogical in the strictest sense means that it does not follow the method of logic, i.e. syllogistic reasoning. An irrational conclusion can be obtained that is perfectly logical. In other words, if the terms of the logical argument are irrational, but the method of reasoning is logical, the conclusion is logical, even if irrational.

I find that within the context of discussion theism, religion, and atheism, rational and irrational; rationality and irrationality are the terms most frequently used when one wants to speak generally about an idea. When one is specifically engaged in a debate, logical and illogical are more relevant to discussing the specific propositions and conclusions within that debate.
 


ChosenByPasta
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Yeah that makes much more

Yeah that makes much more sense now after both of you explained it. Thanks.
Hopefully more will give their take on it.

"Every true faith is infallible -- It performs what the believing person hopes to find in it. But it does not offer the least support for the establishing of an objective truth. Here the ways of men divide. If you want to achieve peace of mind and happiness, have faith. If you want to be a disciple of truth, then search." - Nietzsche


MrRage
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Using a disjunctive

Using a disjunctive syllogism I can make this logical argument:

Premise A: God exists or the moon is made of cheese.
Premise B: The moon is not made of cheese.
Conclusions: Therefore, God exists.

This is a logical argument, but it's also irrational. (The irrational bit is Premise A). Logic is basically the "rules" of making an argument. It doesn't really say anything about your premises, which could be irrational.


Apostate
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MrRage wrote: Using a

MrRage wrote:
Using a disjunctive syllogism I can make this logical argument: Premise A: God exists or the moon is made of cheese. Premise B: The moon is not made of cheese. Conclusions: Therefore, God exists. This is a logical argument, but it's also irrational. (The irrational bit is Premise A). Logic is basically the "rules" of making an argument. It doesn't really say anything about your premises, which could be irrational.

You expressed it very well, in fewer words than I did, and with an excellent example. 


MrRage
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Apostate wrote: MrRage

Apostate wrote:

MrRage wrote:
Using a disjunctive syllogism I can make this logical argument: Premise A: God exists or the moon is made of cheese. Premise B: The moon is not made of cheese. Conclusions: Therefore, God exists. This is a logical argument, but it's also irrational. (The irrational bit is Premise A). Logic is basically the "rules" of making an argument. It doesn't really say anything about your premises, which could be irrational.

You expressed it very well, in fewer words than I did, and with an excellent example.

Sometimes an example is all you need.

I did at one time want to become a mathematical logician, but I was persuaded not to. That was a big mistake.


simian
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another example

Another logical argument:

Premise A: Jesus died to absolve us of original sin, or I have a really big penis.

Premise B: Jesus could not have died because he wasn't a real person.

 

Conclusions: I have a really big penis.

 

Just in case anyone didn't understand the first example.


todangst
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I'd just distinguish them

I'd just distinguish them this way:

 

irrational - a behavior not motivated by reason/deliberation

illogical - an argument that commits a formal or informal error.

 

To be illogical is to misaply logic. To be irrational is to be motivated  not by logic at all, but by an emotion, or perhaps instinct. 

"Hitler burned people like Anne Frank, for that we call him evil.
"God" burns Anne Frank eternally. For that, theists call him 'good.'


RhadTheGizmo
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If illogical, then

If illogical, then irrational.
If rational, then logical.
If logical, not necessarily rational.
If irrational, not necessarily illogical.

While Mr.Rage brings up a good example, I think that his explanation is lacking. Premise A is irrational because it is a disjunction which there is no reason to believe is valid disjunction. It is a disjunctive stated without the faculty of reason (irrational).

If, however, the argument was stated as this:
Premise A: If you accept the bible as true then you must accept the disjunction that either God exists or the Moon is made of cheese.
Evidence: One accepts the bible is true.
Evidence: The moon is not made out of cheese.
Conclusion: One accepts that God exists.

This is a logical construct, as well as the person would be rational if the bible stated that this disjunction was necessary, for the bible would be "reason" for that person.. as well as he would be "exercising reason" to reach his conclusion.

He would however, once again, be irrational if he believed that the disjunction itself is a necessary disjunction to hold for one who does not accept the Bible.


RhadTheGizmo
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Quote: To be illogical is

Quote:
To be illogical is to misaply logic. To be irrational is to be motivated  not by logic at all, but by an emotion, or perhaps instinct.

This is not the only situation where "irrational" can be accurately applied. "Irrational" can also be applied to someone who believes or acts on a construct which is "illogical".


ChosenByPasta
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Yeah, I really don't see a

Yeah, I really don't see a huge difference between the terms, but it's something that has always boggled my mind.

"Every true faith is infallible -- It performs what the believing person hopes to find in it. But it does not offer the least support for the establishing of an objective truth. Here the ways of men divide. If you want to achieve peace of mind and happiness, have faith. If you want to be a disciple of truth, then search." - Nietzsche


MrRage
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RhadTheGizmo wrote: While

RhadTheGizmo wrote:
While Mr.Rage brings up a good example, I think that his explanation is lacking. Premise A is irrational because it is a disjunction which there is no reason to believe is valid disjunction. It is a disjunctive stated without the faculty of reason (irrational).

True, I didn't explain it. I thought it was relatively obvious. But thanks for filling it in.