When is it reasonable to accept the premises of an argument? This seems to be a topic which has been debated extensively in philosophy and one without a conclusive answer. In order to avoid some of these complexities the following is largely taken from Trudy Govier's very practical book A Practical Study of Argument.
According to Govier "When we say that the premises of an argument are rationally acceptable, we mean that it would be reasonable for the person to whom the argument is addressed to accept them." But what if I am analyzing an argument originally intended for someone else? Govier aknowledges this contextual complication but states that it is best to ignore it for our purposes.
"If you can accept—that is, believe—the premises of an argument without violating any standard of evidence or plausibility, its premises are rationally acceptable for you."
But what are these standards of evidence or plausibility? According to Govier, arriving at standards that are applicable to any and all arguments is not achievable due to the scope of premise possibilities. "...premises, like the arguments they are parts of, can be about anything at all-from icebergs near the North Pole to the economy Argentina - or any topic you can think of. Much of the knowledge we need in order to appraise particular premises will be highly specific."
For this reason, Govier provides a list of general standards for evaluating acceptable premises. Though these standards do not provide a clear cut answer, they are useful guidelines for making reasonable a judgement.
Premises is supported by a cogent subargument - If the premise in question is the result of a cogent subargument the arguer has put forward, then it is clearly an acceptable premise.
Premises supported elsewhere - An example of this would be the use of footnotes in research papers indicating that the claim is supported elsewhere. This is an appeal to the authoritativeness of the cited source and as such, depends on whether the authority is a proper one.
Premises known a priori to be true - a priori refers to things which are known independent of experience (as opposed to a posteriori which is knowledge derived from experience or empirical evidence). Claims that are a priori can be known to be true or false on the basis of reasoning or meaning of terms. In other words, they can be proven by logic or reason.
For instance, the statement "No one can steal their own property" is a priori in that it can be proven true by logic alone. On the contrary, the statement "No one can steal the President's property" is a posteriori. To know if it is acceptable we would need to look at supporting evidence such as what kind of property the President has and what safeguards are in place to protect it.
Common Knowledge - Knowledge that is known by most people or is widely believed by most people and for which there is no known evidence against. For example, the statement "Travel by bicycle is faster than walking" is something that is commonly known. It is not necessary or reasonable to insist on proof to support it. Other examples would include claims such as "it snows in the Arctic" or "Canada is north of the United States".
It seems that common knowledge as a guide to premise acceptability is a difficult road to navigate. It is a somewhat vague concept which is very similar to what is known as the ad populum fallacy. With this in mind, I believe common knowledge is more of a tool used to carry an argument forward than it is as a reason in support of a claim whose acceptability is disputed. From the arguers point of view, it acts as a guide in deciding what assertions do not require further support because it is believed they will pass unchallenged as common knowledge. For the audience, it acts as a guide in determining which claims to challenge and which to accept. But if a premise is challenged, then outside the most obvious common knowledge claims such as the examples above, it does not seem to be an adequate response to the challenge.
Testimony - statements based on personal experience or personal knowledge. We can rationally accept a claim on the basis of another person’s testimony unless (1) the claim is implausible, (2) the person or the source in which the claim is quoted lacks credibility or (3) the claim goes beyond what the person could know from his or her own experience and competence.
"If a person claims to have witnessed something that is extremely implausible according to common knowledge or to our own personal related beliefs, the implausibility of the claim provides sufficient reason to question the claim. If the claim is bizarre or crazy enough, the nature of the claim will make us question the testimony—even if we know the person asserting the claim and that person is usually honest, accurate, and reliable."
The credibility of the person testifying can be undermined by various factors such as having a reputation of lying and deceit, an incapacity to make accurate observations, bias or a vested interest in a certain outcome.
A claim which goes beyond what a person could know from his or her own experience or competence should not be deemed acceptable in and of themselves. For instance, if after attending a class a friend told you that the professor has a soft voice, it would be reasonable to accept what she says (provided she is credible) as it is based on her personal experience. On the other hand, if she were to say the professor is the most dynamic lecturer on campus, we could not accept the statement on the basis of testimony alone as it is unlikely she has listened to every professor on campus lecture in order to make a comparative judgement.
Proper authority - "An expert has a special role in the construction and communication of knowledge because he or she has more evidence, a more sophisticated understanding of related concepts and theories, greater relevant background knowledge, and—as a result—more reliable judgment in the particular area of expertise than someone who is not an expert in that field." "The factors that undermine the credibility in contexts of testimony (dishonesty, incapacity to make accurate observations, bias, and vested interest) would also undermine authority."
An especially careful appeal to authority can render a claim acceptable. Such an appeal may be set out as follows:
1. Expert X has asserted claim P.
2. X is a reliable and credible person in this context.
3. P falls within area of specialization K.
4. K is a genuine area of knowledge.
5. X is an expert, or authority, in K.
6. The experts in K agree about P. Therefore,
7. P is acceptable
Accepting premises provisionally -
If you can not judge a premise as acceptable using one of the conditions mentioned above yet you also do not have a definite basis for deeming it unacceptable then it may be useful to accept it provisionally. Provisional acceptance of the premises allows you to move forward to look at the other elements of the argument. If these other elements are satisfactory, then we can accept the conclusion provisionally (if the provisionally accepted premise was acceptable, the argument would be cogent).
A Practical Study of Argument: Trudy Govier
Testing Acceptable Premises in Belief Systems
