14 DAY TRIAL // Suppose you believe something to be true and somebody else thinks otherwise. How can you debate the issue? What is the common ground or how can you find it? And in what sense debating the existence of global warming differs from debating political issues or from debating the existence of God?
Empiric truths are different from moral truths or esthetic truths or religious truths. There can even be said that the word "truth" doesn't have the same meaning in all these situations. There's one thing to say that the Sun rises at a certain hour in the morning, another thing to say that the daylight saving time scheme is a good thing, another thing to say that the dawn offers a beautiful sight and yet another to say that this beauty points to a divine creator.
What are truths?
What all types of truth do is this: they are applicable to a certain domain of imaginable assertions, and they segregate this set of imaginable assertions in two sub-sets. For example the empiric truth segregates the set of all imaginable descriptive assertions into what is likely to happen (or to have happened) and what is not likely to happen (or to have happened). In a limit case, this leads to the segregation between what's possible and what's not possible (but generally speaking anything is possible with some probability).
On the other hand, moral truths segregate the same set of all imaginable descriptive assertions into what is desirable and what is not desirable. Good things are desirable, bad things are not. I suppose we can all see the potential conflict between empiric truths and moral truths: what is desirable to happen may not be very likely to happen (e.g. the end of poverty) and what is undesirable may be quite likely to actually happen (e.g. global warming).
Moral truths range from very trivial examples to the grand questions on good and evil. Many people tend to consider only the "grand questions" as part of "morality", but that's a mistake because there is a continuous transition from the small moral issues to the grand ones. Both the small and the grand moral issues refer to the same thing: to what's desirable and what's not.
Esthetic truths are more general - they apply even to things such as questions. A question may be esthetically appalling in itself, regardless of answer. But a question doesn't have any truth value in the empiric or moral sense - the answer to a question may have, but the question itself isn't true or false. A question can nevertheless be meaningless, in the sense that the possible answers it entitles only resemble the linguistic form of descriptive statements without actually being descriptive statements of anything. For example, many "why?" questions are meaningless, as they ask for the description of a certain reason when no such reason exists. "Why did the dice fall on number 3 rather than on 5?" - it just happened that way, there's no deep reason why. "Why do I exist on this Earth?" - it just happened that way, too (unless maybe you could create some meaning for your life).
But esthetic truths can apply even to nonsensical statements, to questions, exclamations, pictures, music, meteorite shapes, drawings made by monkeys etc. There also seems to be a potential conflict between what's dubbed beautiful and what's considered good and what's likely to happen. You may agree for example that LSD is harmful (empiric statement) and that harmful things are undesirable (moral statement), but nevertheless consider the LSD experience esthetically rewarding. Or can you?
I've been wondering for some time whether we like certain things because we have certain goals or desires, or, on the contrary, we have the goals we have because we happen to like certain things. I tend to believe, in spite of what is perhaps intuitive at first glance, that esthetic feelings are the consequence of goals and not the opposite. For example, certain music may relax me, but this doesn't necessarily mean that I like that music, this effect is not the esthetic feeling itself because I may not want to be relaxed, I may want to "run wild". The esthetic feeling is not the physiological effect something has on the body (including the brain of course), it is a subjective attitude toward this particular effect. In other words, music has a certain effect on me, and then I label the effect as "good" or "bad", "desirable" or "undesirable", and, as a consequence of this moral judgment, I like the music or don't like it. So, I would say that if you like LSD, this points to the fact that you also have some other goals besides that of personal safety (goals that may be more important to you than the goal of personal safety).
Therefore, although they can apply to any kind of statement, regardless of how nonsensical they may be, esthetic truths are not really completely disconnected from the real world. But, again, this doesn't mean we should understand them naturalistically, as being a part of the individual's biology - they are social (and they can be influenced by social factors): they encode in a relatively cryptic way what desires one has. (And they are also instrumental in the evolution of desires and goals.)
The idea that values are prior to esthetic feelings obviously has a lot of practical consequences and changes a lot, from the understanding of small children to the role of the art critique. For example, a small child cries not because (s)he dislikes something but because (s)he doesn't have something (s)he wants (the small child might not yet have esthetic feelings at all). If an art critique says that some painting is beautiful (s)he does this because of the values (s)he has and not simply as a "pure" esthetic judgment. In fact, as I argued above, there are no such things as pure esthetic judgments. Two individuals may disagree whether a piece of art is beautiful either because that piece of art doesn't produce the same physiological effect in both of them or because their moral attitudes toward the induced physiological effect differ (one may consider the effect good, another may consider it bad). So an art critic should probably try to make explicit the values that are embedded in each piece of art.
Besides the empiric, moral and esthetic truths there are two more major kinds of truth (or meanings of the word "truth"): religious truth and mathematical truth. Both these types of truth segregate the set of all descriptive statements according to whether the statements can be deduced from some (more or less) arbitrary statements which are taken for granted (that are "true" by definition or because it seems impossible for them not to be so).
A mathematical proposition is "true" or "false" depending on whether you can prove it within a certain system of axioms (for example the statement "the sum of all angles in a triangle is 180" is true within Euclidian geometry but false within non-Euclidian ones). A religious truth can refer not only to descriptive statements but also to moral ones - one can say that such and such behavior is desirable because (and in this "because" is the difference between religious truth and usual moral truths) this is what some religious text says you should do (or because it is "in the spirit" of that text). Unlike mathematics where you can deduce consequences from the axioms in a unique manner (and everybody agrees what the consequences - the "theorems" - are), religion involves a great deal of vagueness - not everybody agrees what the correct consequences of a certain "sacred text" are.
Why is it so difficult to debate what's true?
One important difficulty arises from the fact that one doesn't usually have in one's head a gigantic set of disconnected statements (although there appears to be a surprising number of such puzzle-brain people). Because of this it is difficult to keep a debate constrained to only some particular issue and to argue solely on that issue - the debate on some issue usually spills over into other related debates which often remain unmentioned.
One has a certain general strategy for generating specific truthful statements, a strategy that can be employed in each particular case to separate what's likely from what's not likely, what's desirable from what's not desirable. If the strategy is used to generate empiric truths, it's called a "theory", if it generates moral statements the strategy is a "moral code" or a "set of basic values". (Please observe that I have a very permissive understanding of what a theory is - this is deliberate. If you could accurately predict the whether by standing on your head, I would have no problem accepting this activity as a valid scientific theory.)
For instance, astronomers don't know how each body in the sky moves, but they have a general theory that allows them to compute the movement of any particular body. Similarly, Christians don't have a preconceived set of all good things and all bad things, they have a set of values that allows them to devise a judgment in each particular case - for example they can have an opinion on stem cell research although obviously this isn't something Jesus is likely to have thought about.
But while there exists a largely accepted method for debating empiric truth - the scientific method - there's no largely accepted method for debating moral truths. (I think that a fairly good candidate for such a method would be the pragmatic method - see Ana Constantinescu's article.) Thus, the temptation is often, especially in the science loving circles, to try to reduce (or express) the unknown in terms of the already known, the unestablished in terms of the established. I.e. the temptation is to say that scientific method can also be applied to moral problems. But unlike many scientifically oriented individuals, I don't believe that moral truths can be discovered by empiric enquiry and reduced to such an enterprise.
The problem with that is that while there exists something, which we call "reality", that's going on by itself, outside of our control, and which we can try to observe and to figure out its mechanisms, there is no such thing as "Morality" - a bunch of moral phenomena just happening outside of our control. A scientific theory tries to describe and predict how real things behave, but moral codes try to influence and change people's behavior. It's a completely different type of adventure.
The only thing that science could do to morality is to get an anthropological view of the subject and to note that various people have different values and that values tend to spread thought society in certain ways and tend to cluster in various ways. This is for instance what memetics is trying to do.
But when people argue about morality they don't argue whether or not some value can spread better than some other value or that some value can spread better in conjunction with some other value. They argue about whether or not it is a good idea to actually follow that as a personal rule of behavior.
Moreover one cannot use science to solve moral issues because the entire scientific method itself, besides the fact that it is highly successful in achieving what it's supposed to achieve, depends on certain values. Foremost, it depends on the idea that it is desirable to know what's going to happen. The debate about this is not a scientific debate. I personally do think that it is highly desirable to know as accurately as possible what's likely to happen in various situations - I think this can tell you what is and what isn't a waste of time. But some think otherwise, they think for instance that predictability ruins beauty and threatens free will. (See article.)
I think that ultimately the debate about values depends on the problem of happiness. We think something is desirable and that a rule of behavior is good if that would eventually contribute positively to our happiness. But insofar we have only a very vague idea about why people are happy or unhappy. We might know what pleasure is or what the causes for depression are but the idea of happiness remains vague. Moreover, different people seem to be made happy by very different things and this prevents that common ground. So, basically the answer to the question "why is it so difficult to find a common ground in a debate?" is that we don't have a very good idea. It's just difficult.