Knowledge and rational persuasiveness

Rational persuasiveness requires that you be justified in accepting the premises of an argument. If the argument is deductively valid, then if you are justified in accepting the premises, you are equally justified in accepting the conclusion. If the premises of such an argument are actually true, then since you know the premises to be true, you know the conclusion to be true.8

However, there are two complications. First, a rationally persuasive argument can be unsound: rational persuasiveness does not itself require that the premises of the argument actually be true. It requires that one be justified in accepting the premises; but, we have seen, it is perfectly possible to have good reasons, to be justified, in holding a false belief. Thus one can be rationally persuaded by an argument but not know the argument's premises to be true. In such a case, one can be rationally persuaded by an argument without thereby acquiring knowledge. Knowledge that an argument is sound, on the other hand, makes a stronger demand on our epistemological relationship with its premises. To know that an argument is sound, we have to know that its premises are true. To know that an argument is sound, we need justified true beliefs in the premises. Whereas for rational persuasiveness, we need only the justification; the belief need not be true.

Second, in the case of an inductively forceful argument that is not defeated, the degree of justification transmitted from known premises to the argument's conclusion may be insufficient to establish the conclusion as knowledge. For the degree of inductive force may be too weak. One might, for example, know with certainty that fifty-one of the hundred stones in a bag are black; one would thus have an inductively sound argument that is rationally persuasive for the conclusion that the next stone drawn at random from the bag will be black. But the argument is only slightly rationally persuasive. Even if that conclusion turns out to be true, the belief in it would be insufficiently justified by the argument, and so would not count as knowledge. More generally, the degree of justification one has for the conclusion of an argument that is inductively forceful but not deductively sound will be smaller than the degree one has for the premises (unless one has some other source of justification for the conclusion).

Let us now look at a case that displays what knowledge is, as opposed to what it isn't. The following scenario provides an example of the requirements placed on knowledge claims:

8 For simplicity we are assuming that if you know one proposition p, and the argument from p to another proposition q is deductively valid, then you know that q. In epistemology this is called the 'Closure Principle'. In more advanced philosophical treatments of these issues, this principle is called into question.

Tabitha Tabloid, a journalist, is at a restaurant one evening and sees a prominent politician at an adjacent table with a person she knows not to be their spouse. 'Perhaps there's a story in this', she thinks. Later, as she walks to her car, she notices a couple locked in a passionate embrace in a parked car that just happens to be parked under a street lamp. On discreet but close inspection she sees that the couple is the politician and their companion. She forms the belief (which happens to be true) that the politician is having an illicit affair with this person. In fact, she believes that the evidence for her belief is sufficiently strong that she persuades her editor that her story should be the next morning's front-page lead.

Here we have the three components that are apparently required for legitimate knowledge claims: a true belief that the politician is having an affair and a rational justification for that belief based upon what Tabitha witnessed in the restaurant and subsequently in the parked car.

0 0

Post a comment