Introduction
Up until now we've spent quite a bit of time looking at the role of biases in argument. Understanding how they influence arguers and our perception of arguments is important; however we're now going to move beyond the psychological aspects of analysis (tell me about your mother...) and start to hone our technical skills.
The first part of our technical analysis involves evaluating whether an argument is strong or weak. A strong argument is one that is convincing for its audience and tough to criticize for its opponents. A weak argument is, well, one that isn't very convincing and easy to criticize. Of course, most arguments are not 100% one or the other, but inhabit a space on the continuum between the two types.
Hopefully, as we learn to recognize the elements of a strong argument, we will learn to incorporate them into our own arguments.
How Do We Evaluate An Argument's Strength?
One thing we can look at to evaluate an argument's strength is who should bear the burden of proof. In simple terms, burden of proof refers to the person an intended audience thinks has to provide an argument for their claim. Before I formally define this term, lets take a step back. Recall that arguments can be decomposed into premises and conclusion(s). A burden of proof can concern the premises or the conclusion, however, lets first focus on the concept as it applies to conclusions.
When we evaluate an argument for burden of proof we are essentially asking if its conclusion is reasonable. That is to say, is it something that most reasonable people (in the intended audience) would accept as true. If the assertion is reasonable, then the opponent bears the burden of proof to show that we should not accept the assertion. If the assertion is unreasonable, then the arguer bears the burden of proof to show (with further supporting premises) why we ought to accept the particular assertion.
When the arguer's conclusion isn't reasonable (i.e., when the burden of proof falls upon the arguer's conclusion), an argument must be made! That is, he's now going to have to back up his conclusion with premises. If, in turn, any of the premises are considered unreasonable, then they too will have to be backed up with further premises. That is, he will also bear the burden of proof to support those premises.
Now we can give a formal definition: A burden of proof speaks to reasonableness of an assertion (be it a conclusion or a premise); the person who opposes whatever is considered reasonable bears the burden of proof--that is, it's up to them to convince us (through argument) that the default position is unreasonable or incorrect. Without a supporting argument, we have no good reason to take their point of view seriously.
Lets look at a few examples to illustrate:
When people deny that the moon landing happened, the burden of proof is on them. They are taking a position against all experts and mountains of physical evidence. The burden falls upon them to show why we should reject the reasonable position of thinking people landed on the moon. The reasonable position is that people landed on the moon; to assume otherwise would require further argument.
When people say that the earth is only 6 000 years old, the burden of proof falls upon them. It's up to them to show why multiple converging lines of evidence are mistaken in their implications and why the theory upon which modern geology and biology are founded is incorrect. It's reasonable to think that virtually all geologists are well qualified to determine what theories do or do not apply to to the age of the earth. To assume a claim that implies that virtually all geologists are wrong requires further argument.
One last note on burdens of proof (laaaaaaaa!):
Historically, burdens of proof can shift. So, what was a reasonable assumption a few hundred years ago might be unreasonable today. We see this with social assumptions. For example, it wasn't too long ago that it was reasonable (for men) to assume that women weren't capable of math and science. Someone (back then) assuming the opposite would bear the burden of proof. Now, that burden of proof has shifted.
Economics is one area where the burden of proof is shifting. It used to be the common assumption that humans are (classically) rational--always seeking to maximize personal interest along the lines of classical mathematical rules. Behavioural economics, interdisciplinary psycho-economics, and socio-economic theory are starting to show these assumptions are wrong. Giving this mounting empirical evidence, the burden of proof is shifting concerning economic models built upon the assumption of (classically) rational agents.
Notice that when burdens of proof shift, it often has to do with accumulation of evidence (and reasons). So, maybe in the future we will discover mountains of evidence that the moon landing was a hoax and that the earth is 6000 years old. If this happens the burden of proof will shift.
Argument Jiu Jitsu
When constructing a strong argument, whenever possible try keep the burden of proof on your opponent. Hai-ya!
Premise Acceptability
Premise acceptability is closely related to issues discussed in burden of proof. Premise acceptability is the degree to which the intended audience for the argument will accept the premises as reasonable. In other words, its an evaluation of how acceptable the premises will be to a particular audience. As I've mentioned a few times already, no matter how air-tight your logical progression from premises to conclusion, if your audience doesn't accept your premises at the start, they'll never accept your conclusion. This is a problem because your conclusion is dependent upon your audience accepting your premises.
Think of it this way: A strong argument merrily leads your audience down the garden path to your conclusion. If they never take your hand in the beginning, they'll never skip along the garden path with you to your glorious conclusion!
The lesson here? (1) When constructing an argument, do your best to make sure the premises are acceptable to your audience. (2) As a critical thinker examining another's argument, ask yourself of each premise if it will be considered reasonable by the standards of your audience.
Logical Consequence (or Logical Force)
Logical consequence or force is the degree to which we are "forced" to accept the conclusion if we've accepted the premises. When we evaluate an argument for logical force, as much as we can, we want to separate this evaluation from the acceptability of the premises. To do this we can ask, "assuming all the premises are true, am I forced to accept the conclusion." Asking this question helps to disentangle the two criteria.
A strong logical argument would be something like this:
(P1) All cats have 4 legs.
(P2) Bob is a cat.
(C) Bob has 4 legs.
If I accept (P1) and (P2), I'm logically forced to accept (C).
A weaker logical argument would be something like this:
(P3) Every time I eat fish, I don't get sick.
(C2) Fish causes me to be healthy.
This logic in this argument is a little weaker for a bunch possible reasons--here are a few: (a) Perhaps I don't eat fish by itself, so maybe it's something else that keeps me healthy--like the tartar sauce I always eat with my fish; (b) maybe it's just dumb luck that the few days following eating fish I haven't happened to get sick; or (c) maybe I only eat fish when I'm already feeling good. For anyone keeping track, this is called the "post hoc, ergo proptor hoc" fallacy. It means, "after, therefore, because of." Or colloquially, "confusing correlation with causation."
It's not a logical impossibility, but the logical connection between the premises and the conclusion is weak. (P3) doesn't compel me to accept (C2). I can accept (P3) without accepting (C2). However, in the first example, if I accept (P1) and (P2), I must also accept (C) or I risk being arrested by the logic police.
Conclusion
As always we can apply this new information in two ways: (1) As critical thinkers criticizing an argument or (2) as clever scholars constructing our own arguments. In both cases we need to be cognizant of the following:
(A) When the arguer's conclusion is unreasonable, he bears the burden of proof to give an argument for why the audience should accept it. (Same goes for the conclusion's critic)
(B) A strong argument will have premises that are accepted as reasonably true by the audience.
(C) A strong argument will compel us through logical force to accept its conclusion if we have accepted its premises.
As critical thinker we should ask of all arguments:
(D) Who bears the burden of proof?
(E) How acceptable (i.e., reasonably true) are the premises?
(F) To what degree does the conclusion necessarily follow from the premises?
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