Some of the ideas commonly cited as logical principles are probably better thought of as matters of argumentative ethics rather than the calculation of logical relations between different statements or propositions. They involve assumptions about how best to go about reasoning with others (which of course includes ideas about how to read and interpret the efforts of others to reason with us). The list of such ideas would certainly include: Burdens of Proof, Ockham’s Razor, and the Principle of Charity as well as some logical fallacies. Many assume that these principles are as much a part of any logical system as anything one might encounter in formal logic (say, the principle of double-negation). Others dismiss these ideas outright. I think it best, really, to regard them as practical decisions which help to facilitate a more productive approach to reasoning. One cannot give the same account of such principles that she might for concepts like double-negation, yet they can help us shape our arguments and our analysis of arguments into something more productive than it would be otherwise.
Burden of Proof: This is the notion that in any given debate, one side may bear more responsibility than the other for producing evidence in favor of its position. This principle is enshrined, for example, in the American legal system wherein we typically regard people as innocent until proven guilty (at least with respect to criminal charges). The notion has also generated a great deal of interest in the philosophy of religion wherein debates between atheists and believers often focus on questions about the responsibilities of each regarding the production of evidence for and against belief.
Much of the issue turns on questions about the (a)symmetry of affirmative and negative propositions. If we take any given proposition (p), the question arises as to whether or not its affirmation (p) is equivalent to its negation (not p). Given that P and Not P are contradictory propositions, this would seem to suggest that the two have equivalent value. If one is true, the other must be false. If it is false, then the other must be true. This would seem to suggest that any given proposition and its negation are equivalent for purposes of logical testing. That argument seems plausible, but it rests on a very formal approach to the subject. It doesn’t take into account some of the vagaries of semantics (questions of meaning) or the practical constraints that may skew the production of evidence and/or the significance that evidence would have in practical reasoning. This is where the case for asymmetry arises (i.e. the view that there are significant differences between the truth value of affirmative propositions and their negations).
One argument for asymmetry rests on the notion that negation (or at least some versions of negation) itself is inherently ambiguous. In some cases, such as predicate term negation, the conditions under which the truth of a negative claim could be established are fairly clear. If, for example someone were to say’ “Dan is in Barrow, Alaska,” I could say no, and I could do so on very definite grounds (i.e. that I am presently on vacation in Azusa, California). In this case, my rejection of the initial claim is based on a very clear condition in which the facts asserted in the claim are not consistent with the evidence at hand. If all negations were so simple, one could as easily accept the burden of proof for negative claims as one could for affirmations. But some negations are more complex than that. If I reject the claim that “colorless green ideas sleep furiously,” I could no longer point to a specific fact that disproves the proposition. Rather, my argument would pertain to the nonsensical nature of the statement itself (which was of course precisely the point of Noam Chomsky’s original presentation of it). Instead of proving the point wrong in any fact-based argument, I would be challenging the meaning the statement, and (if that statement had a legitimate proponent) challenging her to produce something more meaningful before moving on to questions about the factual evidence that would confirm or deny it. For this, and several other reasons, it is sometimes suggested that negation is more problematic than affirmation. To affirm that a statement is true, one must accept as meaningful all of its terms and affirm the state of affairs they describe. In contrast, one may reject a proposition on the basis of other concerns.
On a more practical level, one can point to the difficulties that arise from specific contexts of contested claims. If I assert that one of my students (let’s call him ‘Bill’) cheated on a test, most people would regard it as unfair for me to suggest that it was Bill’s responsibility to prove me wrong. I would normally be expected to put mown reasons for saying this on the table. If I can produce evidence that he did cheat, then it might be fair to expect Bill to answer that evidence. So, for example, if I showed that his essay looked a lot like a Wikipedia entry, I would expect him to show that I was wrong or accept the consequences for cheating. What I could not do is expect Bill to prove that he had not cheated on the test himself without providing any reason to believe he had done so in the first place. (More important, I suspect that in such an example the Dean of Instruction at my college would expect me to produce an account of my reasons for thinking the student had cheated. Only then would she turn to the student for a response to the accusation.)
There is no Bill by the way, at least I’m not talking about one. If any past or future Bill’s read this, no I’m not talking about you. Really, I’m not.
This last example helps to illustrate something else that’s interesting about burdens of proof; it is only one component in a complex dialogue, one responsibility which may (or may not) fall to a particular party in a debate. Once an initial case for the affirmative side in a debate has been made, it is common to expect that a burden of moving the debate forward will pass to the other side. He or she cannot simply sit there and say ‘no, no, no’. At some point, she must address the claims made by others, either by producing a direct case of her own (i.e. proving the affirmative claim wrong, much as one might do in the case of predicate term negation) or by refuting some aspect of the case against her. Another consideration here lies in the way that possession of the burden of proof can also be tied to the privilege of shaping and defining the terms of debate. If I am attempting to prove that Bill cheated, then I am the one putting forward a specific case, applying a specific definition of what it means to cheat to the situation. Bill may take issue with any of these elements (including the definitions I apply to relevant terms), but in all likelihood, the terms of the debate will be set by my efforts to provide an initial case against him. So, the burden of proof is not a uniformly disadvantageous thing to carry into a discussion. It comes with benefits too.
The fact that burdens of proof are themselves subject to debate does provide one significant argument against invoking them. Their role in legal reasoning is set by established conventions, of course, but in less structured contexts such as the aforementioned debates between atheists and theists, questions about who does and who does not have the burden of proof are every bit as troublesome as those about whether or not God exists, who She is, or what sort of church She wants you to go to. So, instead of helping to shape a productive conversation, invoking this principle often serves to provide the sticking point which stops that debate from happening. This doesn’t make the concerns that lead people to argue for asymmetric burdens less valid, but it does serve to suggest that advancing them may not help you communicate effectively with any particular person.
Ockham’s Razor (alt. Occam’s Razor): This principle is attributed to the Franciscan Friar William of Ockham who formulation is usually translated as follows: “Plurality must never be posited without necessity.” Ockham wasn’t actually the first to articulate the principle, and he certainly wasn’t the last, but he was known to use this principle rather often. One of the more common reformulations of the rule reads; “Do not multiply entities beyond necessity.” Perhaps the expression most in keeping with the rule itself is; “The simplest explanation is the best.” Perhaps , we could simply say; “keep it simple stupid.”
…okay, that’s probably too simple.
Anyway, the concept here is that given different alternative explanations for the same thing, we ought to choose the one that makes the fewest assumptions possible. This is sometimes described as the principle of Ontological Parsimony. Now, this certainly doesn’t mean that we should opt for explanations faulty explanations on the grounds that they are often simpler than accurate ones. The idea here is to shed unnecessary assumptions when they do not actually add accuracy to the explanation. It is a rule of thumb that applies when all other things are equal.
Oddly enough, this principle of simplicity raises all sorts of interesting questions about the nature of reasoning in general, and about the practice of scientific explanation in particular, but for our purposes here it is enough to think of it as a good rule of thumb when considering alternative explanations with roughly equal explanatory value. This rule of thumb is not strictly a function of truth-functional relations between propositions, or even about how to weigh evidence. It comes into play only after the evidence is judged to fall equally on two or more theories (assuming that ever really happens), so it is more a question about the practical choices one makes when reasoning than the logical relations between inferences. Hence, its inclusion in this list.
Principle of Charity: The principle of charity comes into play when to interpret another person’s reasoning. As it happens, we can often interpret what another person says in more than one way. If we are talking to them, or otherwise engaging in continuous dialogue (say by email or chat-room) we can sometimes clear this up by simply asking them what they mean, but if we are stuck with a written text and no clear way of soliciting clarification, then sometimes we have to choose between multiple plausible interpretations.
In such cases, the principle of charity would tell us to choose the interpretation that provides the most sound construction of the argument in question. As an extension of this, one ought to refrain from treating an ambiguous text as an argument if the only argument this then produces would then be obviously unsound.
This may seem like another way of telling people to play nice, but the principle of charity is also about ensuring that your own efforts to evaluate an argument are actually productive and useful. Given the opportunity to stick someone with an argument containing an accidental (unnecessary) flaw, will enable one to reject their reasoning, but if that flaw isn’t essential to their point, then the resulting evaluation will apply to a less intellectually useful version of their argument. By contrast, if you construe an ambiguous argument in the most charitable way possible, then should that argument prove unsound, your evaluation will be more decisive. By following the principle of charity, we choose not only to give those whose arguments we consider a better chance of approval, we also ensure that our own time and effort will be spent considering serious thoughts and substantive considerations.
I think the practical nature of this principle is self-evident. It is not strictly a function of logical relationships. One might add that there are clearly circumstances in which people may not wish to follow this rule of thumb. Certainly a Public Relations representative or a lawyer, perhaps even a politician, may gain some ground by exploiting ambiguities in the positions of their opponents. Whether or not that always helps them in the long run is an interesting question, but it seems fair to say that in at least some cases some people may accomplish their own goals better by violating this principle than by following it. In the realm of academic study, this is perhaps less likely than some of these other contexts. (Note that I do not say it never happens in academia, or even that it would never be sound practice to adopt an uncharitable interpretation of someone with an opposing view.) Suffice it to say that there are genuine benefits to following the principle of charity, and that such benefits have led many to recommend some version of it to those new to the subject.
Two additional considerations: Note that the principle of charity does not mean that one ought to improve upon the arguments of others before evaluating them. It sometimes happens that one will hear an argument and realize that you could improve upon it by changing some of its details. You can choose to do this or not as you see fit (perhaps after responding to the argument as it stands), but this isn’t really about the principle of charity. The principle of charity apples only insofar as one is considering plausible variations on the argument one has actually been presented.
Secondly, if a controversy generates sufficient interest in the public, it will produce a variety of different arguments in favor of different positions. When evaluating those positions, one may be confronted with a choice of different arguments with varying degrees of worth. One may even find that the less worthwhile arguments in favor of a position are significantly more popular than the more thoughtful variations. In such cases, I don’t believe there is anything wrong with commenting on the cheaper variations on a theme (it may even be helpful), providing that doing so does not become a substitute for responding to the better and more sound variants. One should also take care to avoid responding to the more thoughtful variations on a stance as though they were producing the cheaper (and more easily dismissed variants). Given sufficient time and space, it is often worthwhile to produce separate responses to the different variations of a position, dealing with each according to its own merits.
Fallacies: Some fallacies can be understood in terms of practical assumptions about the purpose and social context of reasoning.
Ad ignorantiam: These arguments explicitly turns on questions about the burdens of proof required of participants in reasoning. While it is possible to think of the ad ignorantiam fallacy as occurring whenever someone fails to provide a reason for a conclusion, the possibility that burdens of proof may be skewed by the nature of the propositions in question puts this fallacy on the table whenever people raise such questions.
Circular Argument: It’s one of the more interesting features of circular arguments that they actually pass some of the tests of deductive validity (if the premises of a circular argument are true, the conclusion must be true). That should make them valid arguments, right? Still, we don’t think of it that way, and the difference lies in the rhetorical purpose of making an argument in the first place. Simply put, a circular argument fails because it fails to provide a reason worthy of consideration. This is only a problem if we regard the purpose of the argument as one of providing a new reason to begin with. So, this fallacy brings us back to the practical significance of argumentation. It is less a problem of inference relations than a failure of persuasion.