Source: p 44-45, Introducing Philosophy for Canadians: A Text with Integrated Readings (2011 1 ed.)
Preface: If the following is too long to read, read only 1 and 2.
Question: Suppose 1 impossible. Then what can and should an ethical, rational philosopher do? One can politely tell this opponent that he/she is only unreasonably stubborn, self-serving, and defensive, but then what?
Although it might seem to you as if arguments are conclusive, one way or the other, this is almost never the case. An argument can be convincing and persuasive, but there is always room for further argument if someone is stubborn or persistent enough. A good counter- example can always be explained away, and even a large number of counterexamples might be explained away if one is willing to adjust other aspects of the theory, by refining definitions, for example. What ultimately sinks a bad hypothesis or general claim is the weight of the extra explanations it needs. For example, someone argues that there are Martians currently living on earth. You point out that no one on earth has ever seen a Martian. Your opponent explains this away by suggesting that the Martians are invisible to the human eye. You argue that the atmosphere on earth would not support Martian life. Your opponent argues that they are a different form of life, different from any that we can understand. You ask your opponent what these Martians do and how we might come to test his or her view Your opponent says that the Martians don't want us to know that they are here, so they are careful not to do anything that would let us discover their presence. [1.] At this point, you will probably walk away in disgust. [End of 1.] [2.] You have not silenced your opponent. In fact, he or she might go on inventing new ways out of your arguments forever. But, at a certain point, your opponent's explanations will have become so obviously self-serving and defensive that you and everyone else will be completely justified in ignoring them. The point of argument, remember, is to persuade. Absolute proof is impossible. But this means too that persuading some people is also impossible. There are limits to argument—at least, practical limits. [End of 2.]