What makes people irrational thinkers?

[vulcanlogician]

Plato's allegory

Also I want to be careful with Plato's allegory. 

Like all allegories, it's an illustration, and breaks down pretty quickly if taken too far.

The idea that desire and the emotions are somehow discrete and separate parts of the mind, and that there is some objective rational observing "self" watching them from behind (like the chariot guy) is a cartoon picture. The parts aren't detachable, I think.

So it's dangerous to imagine that we can have calculation of pure reason, with the other parts tamped down momentarily.

The allegory is supposed by academics to be a reference to Plato's tripartite soul. An idea he develops elsewhere, like the Republic. The allegory as told in Phaedrus includes flying horses that shoot back and forth between the heavens and the earth... and yet another Platonic theory of reincarnation. My analysis referred to the allegory, but was much more concerned with Plato's well-developed theory of the tripartite soul.

While Plato is wrong ultimately about our minds having three discrete parts, it's interesting to learn that emotions, desires, and rational thinking in fact DO function somewhat independently of one another. Thinking is chiefly done with the prefrontal cortex, desire in the amygdala. Emotion the limbic system (which includes the amygdala, so no clear separating line between the two). So, that's interesting.

But I don't think Plato was really trying to understand how the brain works (like a neuroscientist does). He was referring to what he saw as internal "forces" of the mind that we all have to deal with in life. He saw three of them as distinct and important (reason, passion, and appetite). They aren't really as distinct as he portrays them, but they're "distinct enough" from the first-person perspective (ie. how we experience them).

I think Plato was correct about a number of things: first, he was correct that we are more desirous and spirited than we are reasonable. It isn't just that horses are bigger than the charioteer. He goes into this in the Republic, arguing that our reasonable nature is the "smallest part." Most people in the city are "producers." The producers represent the desirous part of the soul. Fewer in number are the noble auxiliaries... this class represents the spirited part of the soul. Fewest in number are those fit to be philosopher kings: the guardians. They are the least populous class and correspond to the smallest part of the soul, the reasonable part, (the tiny charioteer if you like).

I agree with you (and Foucault) that we don't have a capacity for "pure reason" or "unblemished insight." That's why I added that we need a dialectic process. Either philosophical debate or the scientific method... something that can help us get closer to objectivity. Even Foucault's notion of an epistime is a dialectical criticism that challenges the supposed objectivity of our philosophy, as such. If taken to heart, it gets us closer to realizing what is truly objective.

I disagree with Nietzsche. I tend to think there is one objective truth "out there." It is discernible, intelligible, and we can learn objective facts about it. What I like about Nietzsche is his question "Why not rather untruth?" I think Nietzsche makes a pretty compelling argument that untruth plays an important role in making life worth living. It's pretty much indispensable when you get right down to it. But I also think truth is equally as indispensable. Truth isn't some illusion of my Apollainian nature. It is a genuine thing. What I agree with Nietzsche on is that the Dionysian is important too.