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Tuesday, December 27, 2016


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I’m inclined to agree that human conceivability does not entail logical possibility. The fact that a premise does not appear logically contradictory to the human mind does not entail that the premise is free from contradiction (especially regarding complicated premises), although I'm inclined to believe that conceivability provides a good reason in favor of logical possibility.

But I’m wondering if a problem is lurking. Condition five in the conditions for a rationally compelling argument doesn't seem rationally compelling.

I’ll try to articulate the problem (if it is one -- I'm not sure) in the form of a dialogue:

Smith: So, you hold that a rationally compelling argument must meet these six conditions?

Jones: Right.

S: Conditions one through four are obvious, as is condition six. But what do you mean by “known to be true” in condition five? Do you mean that the premises must be known with certainty? Does knowledge require objective certainty?

(Suppose Jones says “no.” Then condition five might be paraphrased as “It is such that all the premises are recognized as more plausibly true than false.” But suppose Jones says …)

J: I hold that knowledge requires objective certainty.

S: Some competent thinkers would disagree. They’d say that knowledge doesn’t require objective certainty.

J: There’s a reasonable disagreement here.

S: Why believe that knowledge requires objective certainty? Is there a rationally compelling argument for that claim?

At this point, either there is or there is not a rationally compelling argument. If there is, then the argument must meet condition five. But the truth of five hasn’t been demonstrated in a compelling manner.

If there is not, then the discussion remains open concerning the nature of a rational demonstration, and the question of whether or not the modal OA is compelling remains open.

Very intelligent response, Elliot. Whether or not knowledge requires objective certainty, I may re-write condition (5) as

5* It is such that all its premises are objectively certain.

In this way I side-step controversy over whether knowledge requires certainty. I don't need to claim that knowledge requires certainty; all I need to claim is that an argument that issues in a certain conclusion must have certain premises. In fact, I don't need to use 'knowledge' at all.

Toner claims that the existence of God can be certainly known on the basis of the modal OA. Well, then, if there is the least bit of uncertainty with respect to any of the premises, than that uncertainty will be transmitted to the conclusion. Therefore, it is in the spirit of what I am proposing that (5) be re-formulated as above.

If I am told that I 'set the bar too high,' I will reply that I set it in exactly the right place. A rationally compelling argument is one whose conclusion is such that, if you reject it, then you are irrational.

>> all I need to claim is that an argument that issues in a certain conclusion must have certain premises. <<

That is a good point, and 5* seems an apt re-formulation of (5).

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