Insofar as our ignorance of the relevant
issues leads us to be vague in our judgments we manage to enhance the
likelihood of being right.

Increased confidence in the correctness of our estimates can always be purchased at the price of decreased accuracy. There is in general an inverse relationship between the precision of a judgment and its security: detail and probability stand in a competing relationship.

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We estimate the height of the tree at around 25 feet. We are quite sure that the tree is 25 ± 5 feet high. We are virtually certain that its height is 25 ± to feet. But we can be completely and absolutely sure that its height is between 1 inch and 100 yards. Of this we are "completely sure" in the sense that we are "absolutely certain," "certain beyond the shadow of a doubt," "as certain as we can be of anything in the world," "so sure that we would be willing to stake our life on it," and the like.

For any sort of estimate whatsoever there is always a characteristic trade-off between the evidential security of the estimate, on the one hand (as determinable on the basis of its probability or degree of acceptability), and its contentual definitiveness (exactness, detail, precision) on the other. 

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Now this state of affairs has far reaching consequences. It means, in particular, that no secure statement about reality can say exactly how matters stand universally, always and everywhere. To capture the truth of things by means of language we must proceed by way of “ warranted approximation'. In general we can be sure of how things “usually ' are and how they "roughly" are, but never how they always and exactly are. The variety of nature's detail prevents its faithful presentation by the imperfect instrumentality afforded by our symbolic resources.

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The moral of this story is that insofar as our ignorance of the relevant issues leads us to be vague in our judgments we manage to enhance the likelihood of being right, I have forgotten that Seattle is in Washington state, and if forced to guess might well erroneously locate it in Oregon. Nevertheless my vague judgment that "Seattle is located in the northwestern United States" is correct. This state of affairs means that when the truth of our claims is critical we may be well advised to "play it safe" and make our commitments less definite and detailed. We can purchase truth at the price of imprecision.

- Nicholas Rescher

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Cognitive Pragmatism