Post-Hayek and algorithmic information theory, we recognize that information-bearing codes can be computed (and in particular, ideas evolved from the interaction of people with each other over many lifetimes), which are
(a) not feasibly rederivable from first principles, (b) not feasibly and accurately refutable (given the existence of the code to be refuted) (c) not even feasibly and accurately justifiable (given the existence of the code to justify)
("Feasibility" is a measure of cost, especially the costs of computation and empircal experiment. "Not feasibly" means "cost not within the order of magnitude of being economically efficient": for example, not solvable within a single human lifetime. Usually the constraints are empirical rather than merely computational).
(a) and (b) are ubiqitous among highly evolved systems of interactions among richly encoded entities (whether that information is genetic or memetic). (c) is rarer, since many of these interpersonal games are likely no more diffult than NP-complete: solutions cannot be feasibly derived from scratch, but known solutions can be verified in feasible time. However, there are many problems, especially empirical problems requiring a "medical trial" over one or more full lifetimes, that don't even meet (c): it's infeasible to create a scientifically repeatable experiment. For the same reason a scientific experiment cannot refute _any_ tradition dealing with interpersonal problems (b), because it may not have run over enough lifetimes, and we don't know which computational or empirical class the interpersonal problem solved by the tradition falls into. One can scientifically refute traditional claims of a non-interpersonal nature, e.g. "God created the world in 4004 B.C.", but one cannot accurately refute metaphorical interpretations or imperative statements which apply to interpersonal relationships.
The genetic codes (especially their "semantics", the corresponding metabolisms) of plants and animals are examples of such highly evolved structures. We have only very recently achieved some understanding of the syntax of such codes, and grok only a miniscule portion of their "semantics".
Memetic codes, such as legal traditions, are a still more complicated example of such highly evolved structure: dealing with interactions between highly information-rich minds over multiple lifetimes, during which certain actions at the start of life can have irrevocable but not feasibly foreseeable consequences on the rest of a life and on later generations, they typically fall within (a), (b), and sometimes (c). Only a highly evolved tradition can contain the information needed to solve such problems.
We must conclude that "social sciences", "rational ethics", "legal realism", "law and economics", and other such shallowly rational approaches to interpersonal problems can sometimes provide justifications in the sense of (c), but it is a severe misapplication to use them to refute highly evolved traditions. It is much more likley that contradictions between a highly evolved tradition, and a rational analysis of interpersonal problems solved by that tradition, are due to an incomplete axiomatization of the rational theory, rather than due to flaws in the tradition.
The most valuable "theories" about the intersubjective are those derived from the multi-generational epidemioligical experiments that constitute cultural evolution. These are usually not rationally explicable.
As Dawkins has observed, death is vastly more probable than life. Cultural parts randomly thrown together, or thrown together by some computationally shallow line of reasoning, most likely result in a big mess rather than well functioning relationships between people. The cultural beliefs which give rise to civilization are, like the genes which specify an organism, a highly improbable structure, surrounded in "meme space" primarily by structures which are far more dysfunctional. Most small deviations, and practically all "radical" deviations, result in the equivalent of death for the organism: a mass breakdown of civilization which can include genocide, mass poverty, starvation, plagues, and, perhaps most commonly and importantly, highly unsatisying, painful, or self-destructive individual life choices.
Although attempts are often made to justify or falsify intersubjective truths rationally, this hardly demonstrates either (a) the global utility of the rational plan versus current practice, or (b) that the rationalists would have reached the same conclusions had they not already been given by tradition the answers to be derived. Hayek called faith in proximately rational social design a "fatal conceit". The stuff proximate rationalists come up with that is not already in the law is eventually shown to be garbage, although many lives may be ruined before this is discovered. As human culture becomes more homogenous, these intersubjective mutations become increasingly and more comprehensively lethal. Most human effort is now spent repairing the damage caused by these pathological cultural novelties.
Thus, a discovery in social science which contradicts a highly evolved belief is most likely hermeneutically false: ultimately destructive to the individuals or groups who believe it in preference to the highly evolved beliefs. Many radicals even brag about this, about how "dangerous" their ideas are. Tens of millions of victims of torture and genocide of radical, "scientific" ideologies in the twentieth century can testify to this. It is more complete to say that radical plans to change culture are dangerously shallow.
Intersubjective truths can be classified into at least two major groups, transient (proximate, between contemporaries) and traditional (ultimate, or multi-generational). Hayek's canonical example of a transient intersubjective truth is a market price. Most economists think of price in terms of _value_ rather than "truth". But prices incorporate both objective information unknown to other subjects _and_ the values of those subjects. In intersubjective communications, value and truth are inseparably intertwined.
I argue that we should think of highly evolved tradition, what Gadamer calls "hermeneutical truths", in the same way. In one sense, they constitute a kind of "truth", since they can incorporate predictive models of the intersubjective world that are, in principle, achievable from rational thought, but in practice the rational computations and empirical observations would take longer than humans have available. In this sense it is accurate to call highly evolved tradition "truth". But this truth inherently includes the value choices of the various people who have passed on and thus added to a tradition. Many things that are true about the intersubjective world may be lost because they are not valuable. Many trivially untrue things (such as superstitions and myths) may be included because they motivate valuable behavior that reflects deeper but less accessible truths. (Note that "depth" and "accessibility" are the same computational measure, the former across generations and the latter proximate). So it is even invalid to argue _ad absurdum_ (by contradition), to try to falsify subjective traditions by objective standards. Here again, value and truth are inseparably intertwined. Only with purely objective phenomena can value be completely divorced from scientific truth.
Due both to the truth/value intertwining and evolutionary contingency, traditional forms cannot usually be easily reverse engineered. However, due to the depth of multi-generational traditions, we may expect reverse engineering to be somewhat easier than invention or replacement from scratch, if we can come up with the proper methodologies for deconstructing tradition: to tease out truth from value, to determine cultural niches in which traditions flourish and fade, are more valuable or less, are more true or less (three different but related measures), and so on.
Gods are objectively imaginary, but serve as a very useful metaphor for the theory of the intersubjective I have outlined. In other words, God exists -- and belief in Him constitutes a true belief -- intersubjectively, but not objectively. "Omniscience" stands in for the depth of multi-generational experience which cannot be replicated via proximate reasoning; "divine inspiration" is a simple explanation in lieu of understanding the processes of cultural evolution -- most people still don't even understand the relatively simple process of genetic evolution -- and so on. To grossly oversimplify, God is one hell of a computational shorcut. Belief in God propagated because it reflected inaccessible truths about the cultural evolution which actually produced the accompanying ethical systems.
This theory is very simplified and tentative; there are obviously many other aspects of God, and many other religious concepts besides God, which pertain both to cultural evolution itself, and to the truths and values brought to us via that evolution. This is perhaps just a start on an enlightened, scientifically acceptable theology. If objective belief is necessary for the motivational impact of objectively false religious stories, then "God is dead", as Nietchze declared, and in terms of interpersonal relationships we are forced to grope around blindly, unable to either properly accept the given solutions or solve the problems ourselves.
The temptation, often taken, to argue _ad absurdum_ from the objective to the intersubjective makes the continuing motivational effect of a myth problematic in the face of contradictory objective evidence. Also problematic is the equally invalid tendency to argue the other way, against objective findings based on faith in the subjective tradition, as with Creationists. But however invalid, the seeming contradictions between these two different kinds of "truth" have driven many away from highly evolved religious ethics on the one hand, or the findings of modern science on the other.
The theory that religions are evolved rather than divinely inspired (or, rather, that divine inspiration is the intersubjective expression of the objective fact of religious evolution), poses an even more ubiquitous attack to those who argue _ad absurdum_ from the intersubjective to the objective or vice versa. If the human mind is incapable of making this distinction, with at least the fluidity that we reason _ad absurdum_, then our evolved intersubjective truths and values are degraded by the discoveries of objective science (example: atheist Communism), and the attempts to defend valuable intersubjective truths degrade our understanding of objective truths (example: Creationism).
In other words, treat God or the gods as a metaphor for our modern insights into cultural evolution. Indeed, humans did not "create" most of human tradition in the sense of a watchmaker designing a watch. The divine is a brilliant metaphor for the lack of ability of a single mind to rationally understand the functions of traditions.
God as a metaphor for cultural evolution accounts for some of the theological divine traits. Relative to individuals, highly evolved traditions can be practically omniscient (containing much deeper information than the individual could possibly conclude from his immediate experience and reasoning), omnipresent (present throughout a culture), and omnipotent (capable of actions possible only with highly coordinated groups of people).
Lacking local rational justification for particular traditions, we need to develop the kind of awe and respect for highly evolved structures that was once held for God. This involves reconciling a tolerant intersubjective faith in God with the critical study of the objective world. Hermeneutics, the humanistic methodologies for interpreting and applying tradition, should fuse its objective evolutionary understanding of culture with its theological roots, and revive the theological justification for many of our highly evolved interpersonal traditions.
When is it reasonable to use _ad hominem_ and argument from authority in various situations? For example,
-- in a physical science paper, -- in a social science paper, -- in polite conversation, -- in a political debate.
From an immediately rational point of view, these are always invalid methods of debate. However, we are computationally limited creatures, often not capable of anything even approaching full rationality, and so these thinking processes in practice have their place. Even if we were in principle unlimited, but computational resources were not costless, it would sometimes pay to take the computational shortcut of relying on others' judgements. On the other hand, this can be problematic for a variety of reasons, for example when the other parties have strategic reasons for distorting their message.
Examples of the practical use of these decision processes include reputation (of people, brands, etc.) and credentials. In the physical sciences, experiments are usually possible and repeatable, or there are other objective means (such as parsimony) for determining the truth of a statement. However, even when communicating purely objective information, subjective interpretation, selection, etc. quickly creep in, and those not directly observing the experiment must rely in large degree on the authority of the experimenters or theorists. Interestingly, good judgement of authority is based largely on a "meta" understanding, not of the particular science, but of the scientific method itself: is the theory falsifiable and parsimonious, are the experiments repeatable, are the statistical methods valid, and so on. Much scientific misinterpretation, and much of decisionmakers' lack of scientific understanding, may be remediable by improving understanding of scientific methods themselves, rather than improving understanding of the results of particular sciences.