It's become clear that our ability to reason our way to the truth is something of a side effect of the function of reasoning, which is mostly to win arguments. Consequently, if you want to actually figure out what's true, you have to be able to put hacks in place that defeat your inbuilt tendency to confirmation bias and many other reasoning errors that humans make. Rationality communities like Less Wrong are great places to level up your rationality.
One of the basic things to do when trying to figure out the truth is to know your own predisposition; and specifically, know what you want to be true. Not only did reasoning develop for less-than-pure-truth-seeking purposes, but it's very goal-directed: we humans tend to start out with the end in mind, and build a bridge to it by any means necessary. (If you want a more academic phrasing to this, Stephen Toulmin codified how humans empirically argue, whether or not that's how they get to the truth.) Even in science we do this - the innovation is that we try to avoid problems by identifying the end in mind as explicitly provisional, and we have a name for this (a hypothesis). Of course history is full of people who wanted to believe something too much, and forgot that what they were using was a hypothesis. (Really all beliefs should be hypotheses, as long as it's possible to believe something that's not true, which it always is. Of course it's very very difficult to walk around dealing with everything as provisional.)
That what you want to believe can steer you wrong was highlighted for me in the recent online debate between anthropologist John Hawks and Jerry Coyne. The point of contention was the admittedly esoteric taxonomical question of whether humans are apes. Since Hawks's expertise is closer to the subject than Coyne's, and my eyes glaze over on these kinds of details, I should be inclined to take Hawks's position, which is that we are not apes. But I have to admit to myself that I want us to be "apes", because to someone interested in evolution, that's kind of cooler to say, since it seems to more dramatically link us to other animals. (More than "hominoids" anyway, since there's only one surviving species, unless you count Slayer separately.) His explanation is in this post; basically it comes down to the rules of taxonomy and the difference between mono-, para-, and polyphyletic taxa, and it's the same reason birds aren't dinosaurs, and all land vertebrates are not fish.
The point is this: without admitting to myself honestly and explicitly that I wanted the answer to be that we're apes, I might have let myself take a different position. For the vast, vast majority of things we will think and decide about in our lives, we will want one option to be true right out of the starting gate. And of the few things where we don't want something to be true ahead of time, for the majority of them, it's not that we're being neutral, it's that we just don't give a damn either way. Dispassionate discourse takes effort!
USA PATRIOT Act
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