Insofar as belief is voluntary, people can have various motives for the things that they think and say. This is not only true in the sense that people can have different motives for different beliefs, but also in the sense that there may well be a mixture of different motives for any particular belief.

People tend to notice such motives in others, but it is rather unusual for them to notice the motives in themselves, rather than simply to think that the reason that they say or think something is that it is true. Thus Robin Hanson reveals an extraordinary degree of self knowledge when he discusses his reasons for having opinions:

Decisions – Sometimes I need to make concrete decisions where the best choice depends on particular key facts or values. In such cases I am forced to have opinions on those subjects, in order to make good decisions. I may well just adopt, without much reflection, the opinions of some standard expert source. I have to make a lot of decisions and don’t have much time to reflect. But even so, I must have an opinion. And my incentives here tend to be toward having true opinions.

Socializing – A wide range of topics come up when talking informally with others, and people tend to like you to express opinions on at least some substantial subset of those topics. They typically aren’t very happy if you explain that you just adopted the opinion of some standard expert source without reflection, and so we are encouraged to “think for ourselves” to generate such opinions. Here my incentives are to have opinions that others find interesting or loyal, which is less strongly (but not zero) correlated with truth.

Research – As a professional intellectual, I specialize in particular topics. On those topics I generate opinions together with detailed supporting justifications for those opinions. I am evaluated on the originality, persuasiveness, and impressiveness of these opinions and justifications. These incentives are somewhat more strongly, but still only somewhat, correlated with truth.

Exploration – I’m not sure what future topics to research, and so continually explore a space of related topics which seem like they might have the potential to become promising research areas for me. Part of that process of exploration involves generating tentative opinions and justifications. Here it is even less important that these opinions be true than they help reveal interesting, neglected, areas especially well-suited to my particular skills and styles.

As Robin notes, even when we have motives which are distinct from the truth, they may promote truth to some extent. Thus for example if someone wishes to be respected, this is not the same as being motivated by the truth, but it may require believing the truth to some extent. Thus for example Gene Ray probably did not earn much respect with his Time Cube website. On the other hand, depending on context, the desire for respect will sometimes conflict with truth and lead us away from it.

To the degree that we wish to speak or to believe the truth, this motive will work against motives in conflict with the truth and in favor of motives that favor the truth. And likewise, to the degree that we care less about speaking or believing the truth, other motives will tend to predominate. Now there are two reasons why people desire truth: for its own sake, and for the sake of other things, as in Robin’s case when he desires the truth for the sake of making a good decision.

In principle a useless truth may be more desirable than a useful truth, but this does not necessarily mean that people desire the useless one more in practice. Thus for example many people say that philosophy is useless, not meaning by this that it is more desirable than other branches of knowledge, but much less. Francis Bacon is a good illustration of this in his Novum Organum:

LXXIII. Of all signs there is none more certain or worthy than that of the fruits produced, for the fruits and effects are the sureties and vouchers, as it were, for the truth of philosophy. Now, from the systems of the Greeks, and their subordinate divisions in particular branches of the sciences during so long a period, scarcely one single experiment can be culled that has a tendency to elevate or assist mankind, and can be fairly set down to the speculations and doctrines of their philosophy. Celsus candidly and wisely confesses as much, when he observes that experiments were first discovered in medicine, and that men afterward built their philosophical systems upon them, and searched for and assigned causes, instead of the inverse method of discovering and deriving experiments from philosophy and the knowledge of causes; it is not, therefore, wonderful that the Egyptians (who bestowed divinity and sacred honors on the authors of new inventions) should have consecrated more images of brutes than of men, for the brutes by their natural instinct made many discoveries, while men derived but few from discussion and the conclusions of reason.
The industry of the alchemists has produced some effect, by chance, however, and casualty, or from varying their experiments (as mechanics also do), and not from any regular art or theory, the theory they have imagined rather tending to disturb than to assist experiment. Those, too, who have occupied themselves with natural magic (as they term it) have made but few discoveries, and those of small import, and bordering on imposture; for which reason, in the same manner as we are cautioned by religion to show our faith by our works, we may very properly apply the principle to philosophy, and judge of it by its works, accounting that to be futile which is unproductive, and still more so if, instead of grapes and olives, it yield but the thistle and thorns of dispute and contention.

If there are two questions about reality, and people care about the truth of the matter equally in itself, but one of the questions will also be useful for other things, then people will be motivated more to discover the truth about the useful matter. Thus Bacon here suggests that he only cares about truths which are useful for other things, and not at all about useless truths.

From the point of view of natural selection, there is a good reason why people could be expected to search out useful truths more than useless truths. For useful truths are of course useful, and consequently more likely to lead to survival and reproduction, than useless truths.

Bacon is wrong in his opinion here, considered as a question of ethics and philosophy. Nevertheless, he is hinting at something true when he rejects the kind of philosophy which yields “but the thistle and thorns of dispute and contention,” and when, in the preface to his book, he not so subtly mocks the academic system of the time:

We make no attempt to disturb the system of philosophy that now prevails, or any other which may or will exist, either more correct or more complete. For we deny not that the received system of philosophy, and others of a similar nature, encourage discussion, embellish harangues, are employed, and are of service in the duties of the professor, and the affairs of civil life. Nay, we openly express and declare that the philosophy we offer will not be very useful in such respects. It is not obvious, nor to be understood in a cursory view, nor does it flatter the mind in its preconceived notions, nor will it descend to the level of the generality of mankind unless by its advantages and effects.

Bacon is suggesting here that “the system of philosophy that now prevails” is itself correctly understood as something useful, not as something useless. It is useful for “encouraging discussion,” for “embellishing harangues,” for “the duties of the professor, and the affairs of civil life.”

In other words, Bacon is pointing to motivations much like Robin’s motivations of socializing, research, and exploration, motivations not entirely correlated with truth. We could rephrase Bacon’s critique as something like this:

“No one is interested in truth in itself. Today’s philosophy is interested in impressing and pleasing people and in other such things. No truth at all is necessary to accomplish these tasks, and thus there is no reason to suppose there is any truth in today’s kind of philosophy. I am myself not interested in truth in itself, but at least my philosophy will attain real truths, because I will use it to accomplish physical tasks that cannot be accomplished without at least some truth about physical reality.”

This goes too far, but there is a good deal of truth in it. I will consider this in more detail in another post.