And now for my incoherent ramblings.
My definitions: (anything here is not in the MBTI sense of the word)
Rational - the ability to perceive clearly and make judgments accordingly; sanity
Emotions - instinctive or intuitive feeling; largely subjective
Logic - formal deductive reasoning; largely objective
To begin, I would like to propose that Logic and Emotions both intersect with parts of the overarching judgment-making ability known as Rationality. To be rational is to perceive and reason clearly. To speak of rationality, logic, and emotions is to speak of objectivity and subjectivity. Rationality strongly implies objectivity. Logic follows much of the same route. Emotions, however, are subjective. (albeit influenced by objective factors) Therefore, it would appear that logic is closer to true rationality than emotions are. However, it would be most fallacious to, at this point, state that emotions are inherently irrational. Emotions tap into an inner wealth of information that cannot be reached by logic alone. This information call allow one to see more aspects of a situation, including the ones not externally apparent. "This makes me feel sad." How can one objectively quantify that? Is the statement wrong? It is not. Using objective reasoning, logic, one can reach a conclusion using this most subjective input. To ignore this dimension of input would be irrational as it excludes part of the picture from which a rational judgment is to be based off of. Conversely, to act in an illogical manner off of these feelings would be equally irrational as it would not be a judgment made through a "clear" thought process.
To conclude, emotions and logic, when used together properly, naturally compliment each other. Without the other, a degree of rationality is lost. For this reason, both elements must be included, with balance, in order to be rational.
Edit: As a last note, the key is to interpret emotions, not ignore them.
On the other hand... letting them get carried away can be just as bad, or worse. There's been more than one war started by blind hatred or love, working on emotions without them being tempered with reason can go very badly.
Want to see whot happens when yeur emotions run rampant without any intelligence to back them up at all? Watch a soap opera, see people throw tantrums and 'get back at' each other off imagined slights, without putting any time into reason at all. Watch them destroy their best friends' life simply because they are in a bad mood. This is a prime example of 'humans' being no more valuable than animals, for supposedly being 'smarter', alot of the time we don't use our brains -_-;;
Of course the other hand can be almost as bad, turning one into a cold emotionless machine with zero sympathy or understanding. Sadly I tend to trend more towards this side than the other, I'd like to maintain a healthy balance but it's alot harder than one would think.
Short answer is yes, emotions do screw up rational thought, because they are literally the exact opposite of it, however they're also needed to some extent. The trick is just letting them have some effect without letting them run rampant without a leash.
Anything. Basically, an irrational decision is one made without making any consderations at all. A decision to kill one's self based on a sense of overwhelming feeling- that's irrational.
Emotions are a bit more defined and agreed upon. You can make irrational decisions based on emotions, yes. There is probably a bigger chance of making a "wrong" decison based on emotions than making a "wrong" decision based on pure logic. But do they always? No.. You can have strong emotions that can aid in making a very sound and rational decision.
Depends on the person and their intelligence level and their maturity and their upbringing and so on..
So, do you think emotions are actually the cause of that irrational behaviour? Or is it just the lack of consideration that causes it, regardless of emotion?
Either way, it certainly gives the appearance of emotions as the cause.