If we all have personal biases (ie. every individual, being unique, perceives the same event slightly differently), how can we trust anyone to provide the real truth?

An incomplete answer, but relevant, I hope.

Suppose the question is: did Prof. Geisler show up for class on Monday? We ask students enrolled in the class. All the students who were there in the room at class time say yes: Prof. Geisler was there. In fact, she arrived on time, and taught a full class.

Let's grant that every person in the room had a slightly different take on exactly what went on in the room at that time. Let's also grant that some of what some people would say happened will be inaccurate, and may reflect their biases and psychological idiosyncrasies. The question, however, is whether Prof. Geisler showed up. There's no reason to think these differences in perception got in the way of judging that.

In one way this is a trivial example, but it reflects something extremely common. Even with our very real quirks and biases, there's an enormous amount of what we perceive and believe for which those quirks and biases are simply irrelevant. Individually, most of these facts may be inconsequential. But when we add them up, we arrive at a shared account of a great deal about the way things are. We don't all live in our own separate worlds. People who claim otherwise strike me as either not really thinking through what they're saying or else in the grip of a bad theory.

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