Can you draw a distinction between the words "unrational" and "irrational" [Details]?

From what I have read, the usage in interchangeable. Which you use should depend on the origin of the root word. If it has its basis in Latin, you should use “in”, if Germanic then “un”.

You may have discovered some previously inknown concep but t I think that it may be unsignificant in the overall scheme of things.

Frankly, I have never seen the use of “unrational” before today. I have only used (and seen) “irrational” or “not rational”.

It’s a silly formation that doesn’t make much sense. Just because one can doesn’t mean one should.

You rarely see or hear the word “unrational” in everyday use. In fact upon hearing it, your ear trips the mental switch to pull out the red pencil. To me, the only justification for using the word would be as means of DELIBERATELY distinguishing the matter discussed from the more familiar and accepted “irrational”. So in my mind irrational would be “without reason”, while unrational is more deliberate or “against reason”.

Exactly my thought, @stanleybmanly. Excellent definition.

Deliberate nuance.

As in:
The Search For Unrational Leadership: Using Rational And Irrational Methods To Change Your Life
and
The Mystique of Enlightenment: The unrational ideas of a man called U.G..

I have not come across the word unrational, but I have seen non-rational used to mean a decision not grounded in reason. There is a subtle difference from the word irrational, which means go against reason. If I act from intuition then I could be said to be acting non-rationally but not irrationally.

Although they are theoretically interchangeable, I would probably only use. unrational in a context that describes something outside the boundaries of rationality, and use irrational to describe something counter or contrary to rationality.

How rational is the process of splitting hairs, anyway!

There is a similar distinction between immoral and amoral.
http://grammarist.com/usage/amoral-immoral/

Being listed on Dictionary.com doesn’t really prove anything because dictionaries are descriptive, not prescriptive. They are reference works to help people understand how words are used, whether correctly or incorrectly. (That’s why it made no sense for people to freak out when dictionaries started making note of the incorrect use of “literally” to mean “figuratively.” There was some strange idea that putting it into the dictionary legitimized it, when all dictionaries have ever done is record usage, both good and bad.)

The books don’t really prove anything, either. The author of the first one says he made up the word, and also defines it as being more or less synonymous with “arational.” And the second one is a self-published PDF that only uses the word in the title (though again, the content looks to be more about arationality). In both cases—assuming the second author isn’t just ignorant—it’s a deliberate coinage for a specific, rarefied purpose. There’s no pretense in either of it being an ordinary word.

And as @rojo pointed out, “unrational” violates the normal rules of English (since “rational” and its related words are of Latin origin). Searching into it further, I can only find any regular usage of the word in middle English, which was highly irregular and technically a separate language from what we speak today (i.e., modern English).

Note also that neither “rejecting ration” nor “lacking ration” make any sense as definitions because the “ration” of “rational” and “irrational” is a component, not its own word that is being modified. While there is an English word “ration,” it is not any part of “rational” and “irrational.” Instead, those words are using the Latin word for “reason.” So really, you would want to say “rejecting reason” and “lacking reason.”

But even that doesn’t work because you simply have a mistaken understanding of the connotation of each word. Even if we use the examples you have provided, “unrational” does not mean “rejecting reason.” Your examples make it out to be a synonym of “arational,” which means “not based on reason.” So “going with your gut” might be arational, even if it is not irrational (which means “against reason,” and would include “rejecting reason”). Really, if you want to mean “lacking reason,” then “arational” or “non-rational” would be more appropriate. But if you are trying to imply “rejecting reason,” then “irrational” is definitely the word you are looking for (no “ifs,” “ands,” or “buts” about it).

And yet, @JeSuisRickSpringfield, of 7 jellies, only @zenvelo denied there was a distinction between (as @stanleybmanly nicely defined) without reason and against reason.

I appreciate the essay, but if unrational isn’t allowable on (not a word) Fluther, then why is there even this question?

The mathematician in me has been reckoning this thread.

Unrational would be a state where one could not find a relationship between two things. Irrational is where one cannot define something as the relationship between two things.

Rational is something that is equal to the relationship between two things.

For me and my purposes, @zenvelo, @stanleybmanly defined it more clearly than I did.

The quarterly, June 2015, update to the OED added 500 new words, phrases, and senses, so new definitions are constantly popping up.

But, of course, as @JeSuisRickSpringfield points out, the OED is just another mindless knee-jerk opinion poll.

Whether valid or not, the times being as they are, a great deal of use can be made of a single word defined as “against or contrary to reason.” The old pejoratives like dumb or stupid don’t do justice to the fashionable rage in this country around denying reality!

I agree, @stanleybmanly.
We’re living in very unrational times. The current state of the US Presidential election is contrary to reason. Reality TV has overtaken reality.

@ibstubro Consider the possibility that seven jellies can be wrong. Facts aren’t made by committee. So I get that what @stanleybmanly said is what you were trying to say, but that doesn’t mean you were successful in saying it. I can try to convey my feelings about some topic by saying “it makes me feel oop ba loob a bing,” but I’ll be lucky if that comes across. And by the way, “fluther” is a word. It is the collective term for a group of jellyfish (similar to a murder of crows or a school of fish). That’s why we have the whole ocean theme and call each other “jellies.”

@stanleybmanly We have a word for “against or contrary to reason.” That’s what “irrational” means.

To me, unrational would mean NEVER rational while irrational would mean NOT ALWAYS rational.

@JeSuisRickSpringfield. Yes, but I think the need has arrived to narrow the definition for the fad sweeping the country. I’m content with the word irrational in front of fear for example, but when folks like Mitch McConnell & his Republican posse talk about the “hoax“of climate change…..irrational is no longer adequate. It’s like labeling a brontosaurus a lizard. Irrational is now a word that a growing segment of our population no longer recognizes as derisive, as the numbers shrink of those capable of spelling it let alone proffering a reasonable definition.

@stanleybmanly I see your point. But in that case, you are looking for a word that means something like “the complete abandonment of reason” or even “rejecting reason as a basis for evaluation.” That’s interesting, and I could see the usefulness of having a single word to sum up that kind of attitude. It would definitely be a new coinage, however, and would take us away from what @ibstubro is talking about. So while there might be a gap in the language that “unrational” could fill, it’s not the place where he is trying to stick it.

That’s it. There should actually be no more powerful accusation against an argument, position, etc. than “it is irrational”. Even the charge of “dishonest” should not supersede it, because there is at least logic involved with corruption. Self aggrandizement makes sense! Returning to the charge of climate change “hoax”, while those hearing it might well perceive such a statement as patently dishonest, the person issuing it is let off the hook with the charge of it being irrational. In other words irrational is dissociated from the possibility of being deliberate. The implication being ” he doesn’t know any better.” While McConnell is merely representing the interests of the coal companies who sharecrop out the state of Kentucky, “irrational” allows him (like “I’m no scientist”) to hide behind the blind of “I’m every bit as ignorant as the folks tricked into sending me here.”

6 out of 7 jellies and Dictionary,com understanding the meaning I intended convey are sufficient for me, @JeSuisRickSpringfield. If someone can’t intuit and refuses to reference, that’s beyond my control.

As usual, I don’t understand your intense investment in proving me wrong. It appears irrational.

@ibstubro I’m afraid I don’t understand what you mean by “as usual.” By my count, this is only the second disagreement we’ve ever had. And the other wasn’t even much of a disagreement (though it was also about a linguistic mistake on your part). I also think you are too hung up on “understanding the meaning you intended to convey.” Your question asked us to draw a distinction, so I did. And it is the linguistically correct distinction to make. But I’m not saying that if you used the word in conversation I wouldn’t understand what you meant. I’m just saying that technically you aren’t using the correct word. And really, you’re not in any position to deny this since you have already admitted that you needed us to “intuit” what you “intended.” If you had used the correct word, we wouldn’t need to use those interpretive tools.

Do you have something larger riding on this? Because I can’t really figure out why you’re so wound up about this.