All of human knowledge comes from experience, and all experience is first derived from the senses. Aristotle describes this process at the beginning of his Metaphysics:

All men by nature desire to know. An indication of this is the delight we take in our senses; for even apart from their usefulness they are loved for themselves; and above all others the sense of sight. For not only with a view to action, but even when we are not going to do anything, we prefer seeing (one might say) to everything else. The reason is that this, most of all the senses, makes us know and brings to light many differences between things.

By nature animals are born with the faculty of sensation, and from sensation memory is produced in some of them, though not in others. And therefore the former are more intelligent and apt at learning than those which cannot remember; those which are incapable of hearing sounds are intelligent though they cannot be taught, e.g. the bee, and any other race of animals that may be like it; and those which besides memory have this sense of hearing can be taught.

The animals other than man live by appearances and memories, and have but little of connected experience; but the human race lives also by art and reasonings. Now from memory experience is produced in men; for the several memories of the same thing produce finally the capacity for a single experience. And experience seems pretty much like science and art, but really science and art come to men through experience; for ‘experience made art’, as Polus says, ‘but inexperience luck.’ Now art arises when from many notions gained by experience one universal judgement about a class of objects is produced. For to have a judgement that when Callias was ill of this disease this did him good, and similarly in the case of Socrates and in many individual cases, is a matter of experience; but to judge that it has done good to all persons of a certain constitution, marked off in one class, when they were ill of this disease, e.g. to phlegmatic or bilious people when burning with fevers-this is a matter of art.

Since our knowledge depends on the senses, to the degree that knowledge becomes more remote from the senses, it becomes harder to know the truth. But more remote in what way? More remote precisely in being less directly derived from the things that we sense. Thus for example Descartes provides an example of a particularly ridiculous error when he says in his Principles of Philosophy,

Fourthly, if body C were wholly at rest and were slightly larger than B, whatever the speed at which B were moved toward C, it would never move this C, but would repelled from it in the contrary direction; because a body at rest resists a great speed more than a small one, and this in proportion to the excess of the one over the other, and, therefore, there would always be a greater force in C to resist than in B to impel.

In other words, if a smaller object hits a larger object, the larger object will not move in any way, but the smaller one will rebound in the opposite direction. How false this is does not need to be argued, and this precisely because of its closeness to the senses.

Sometimes a distinction is made between empirical and non-empirical knowledge, but in truth there cannot be a rigid distinction between these two things, because all of our knowledge is empirical, and thus there can only be differences of degree here. Thus for example the question of whether there is meaning in the universe might be considered a philosophical rather than an empirical issue, but we have given empirical reasons for thinking that there is.

But again, to the degree that a certain matter is more distant from the senses, it will be more difficult to know the truth about that matter, and consequently people are more likely to make a mistake about it. This happens in two ways.

In the first and more obvious way, when it is more difficult to test the matter with something sensible, as we might test Descartes’s claim about a smaller body hitting a larger body, it is easier to fall into error without there being a simple way to correct that error.

The second way is less obvious, but follows from the discussion about beliefs and motivations. If some fact about the world makes a big difference in our sensible experience, then we will be interested in knowing that fact, in order to be able to affect our experience. If a stove is hot, touching it will be painful, so it is important to know whether the stove is hot or not. Thus, for the sake of such purposes, people will be interested in knowing the truth about matters close to the senses. But if some fact does not seem to affect our sensible experience much, then people will care less about knowing the truth about that matter, since they do not need to know it in order to affect their experience. This implies that other motives, motives distinct from the desire for truth, will affect their beliefs in these matters more than in matters closer to the senses. And insofar as they are more affected by motives that can lead away from the truth, they will again be more likely to fall into error, this time without a strong desire to correct that error.

Taking these two ways in combination, people will fall into error more frequently in matters that are more distant from the senses, and in such situations people will have neither a great desire of correcting the error, nor an easy way to do so.

If we compare these somewhat theoretical deductions with experience, they are verified fairly well. There are various matters where there is much more disagreement than in other matters. For example, there is much more widespread disagreement in religion, theology, philosophy, politics, ethics, economics, and so on, than there is in mathematics and physics. We can easily see that the areas with more widespread disagreement are the ones more remote from the senses. Someone might say that politics, ethics, and economics are not remote from the senses, but if we consider the fact that all of these topics involve moral issues, we can see that they are in fact remote in the way under consideration, namely that it is not easy to subject them to sensible tests. And on the other hand, where there is disagreement in physics, it is likely to be in matters where it is hard for the difference to make a difference to the senses, as for example in interpretations of quantum mechanics.

Greater disagreement, of course, does not demonstratively prove the existence of more error, since even when there is agreement, there can be agreement on something false. But it strongly suggests the existence of more error, since disagreement cannot exist without someone being wrong, whereas agreement can be without anyone being in error. And in the areas mentioned, disagreement is so widespread that there is necessarily a great deal of error in those matters.

And these areas are also areas where we can see that people’s opinions are strongly affected by motives distinct from the desire for truth, as was suggested by the theoretical account above. Some indications of this:

First, in such areas people tend to form into various groups or “schools”, where the majority of a whole body of opinions are accepted. This happens more in religion and in politics than in the other examples, but the tendency is apparent in the other cases as well. If people were influenced only by the desire for truth, we could expect a somewhat more even distribution of opinion, where intermediate positions would be more common. Instead, the actual situation suggests that people have a desire to fit into certain groups, and to some extent adopt their opinions in order to favor this result.

Second, arguments in such areas tend to be more emotional than arguments about matters which are more easily tested. If an argument is witnessed by outsiders who have no understanding of the topic, and one of the participants is much more emotional than the others, the outsiders will tend to presume that the less emotional participant is more likely to be right. And this is for a good reason, namely that the emotions are moved more by sensible goods, rather than by truth in itself, and consequently someone who is very emotional about some intellectual issue is likely being moved by desires other than the desire for truth.

Third, related to the second reason, conversations about such matters are much more likely to be “bad conversations” of the kind noted in the previous post. They are much more likely to result in anger and insults, and in the belief that one’s conversational partner is not of good will, than conversations about mathematics. Thus for example many people accuse others who do not accept their religion of being of bad will, as for example in this blog comment:

For Pete’s sake, a simple self-educated layperson like myself has engaged in countless debates about the historicity of the Resurrection, both in person and on websites such as this one, and have not only come out on top every single time, but have yet to ever hear presented (not even once!) a decent case contra that cannot be demolished with minimal effort. The solidity and strength of the pro arguments, coupled with the pathetic weakness of all proposed alternative explanations, are what have led me to the (unwilling) conclusion that it takes an active act of will to reject them, and that unbelievers are, as in the words of Saint Paul, “without excuse”.

Likewise, it is very common for people to consider others who disagree with their politics to be bad people. Thus for example Susan Douglas writes,

I hate Republicans. I can’t stand the thought of having to spend the next two years watching Mitch McConnell, John Boehner, Ted Cruz, Darrell Issa or any of the legions of other blowhards denying climate change, thwarting immigration reform or championing fetal “personhood.”

After some discussion, she concludes the post:

Why does this work? A series of studies has found that political conservatives tend toward certain psychological characteristics. What are they? Dogmatism, rigidity and intolerance
 of ambiguity; a need to avoid uncertainty; support for authoritarianism; a heightened sense of threat from others; and a personal need for structure. How do these qualities influence political thinking?

According to researchers, the two core dimensions of conservative thought are resistance to change and support for inequality. These, in turn, are core elements of social intolerance. The need for certainty, the need to manage fear of social change, lead to black-and-white thinking and an embrace of stereotypes. Which could certainly lead to a desire to deride those not like you—whether people of color, LGBT people or Democrats. And, especially since the early 1990s, Republican politicians and pundits have been feeding these needs with a single-minded, uncomplicated, good-vs.-evil worldview that vilifies Democrats.

So now we hate them back. And for good reason. Which is too bad. I miss the Fred Lippitts of yore and the civilized discourse and political accomplishments they made possible. And so do millions of totally fed-up Americans.

As I stated in the post on beliefs and motivations, it is not difficult for people to notice that motives other than the desire for truth are influencing other people, but they tend not to notice those motives in themselves. In a similar way, many people will have no difficulty admitting that the point of this post applies to other people, but will have a much harder time admitting that it applies to themselves.

Of course it is true that some people have more of a desire for truth in itself than other people. And the stronger this desire in a person, the more likely the person is to hold the true position in any of these matters. But it is not credible to suppose that people are actually divided in the “good-vs.-evil” way that Susan Douglas says that Republicans divide people, and in which she herself divides people. If I were a Mormon, for example, it would remain absurd for me to suppose that Mormons are good people and that everyone else is bad, or that Mormons are reasonable people and that everyone else is unreasonable. Given the premise that Mormonism is true, it would follow that a person more interested in truth would be more likely to adopt Mormonism. But it would not follow that Mormons overall have a different nature from other people, nor is this credible in the slightest.

In other words, of course there are true positions in religion, theology, philosophy, politics, ethics, economics, and so on. But overall people’s motives are more affected by non-truth-related motives, and by only-somewhat-truth-related motives, in these matters than in matters closer to the senses, and they are therefore more likely to fall into error in the areas more remote from the senses. Now you might personally hold the true position in some of these matters, or in all of these matters. Or perhaps you don’t. Likewise, you might personally care more about the truth than other people do. Or perhaps you don’t. Either way, there is little reason to suppose that the point of this post does not apply to you.