5004
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We can know basic Principles without further knowledge, but not the other way round [Descartes]
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Full Idea:
It is on the Principles, or first causes, that the knowledge of other things depends, so the Principles can be known without these last, but the other things cannot reciprocally be known without the Principles.
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From:
René Descartes (Principles of Philosophy [1646], Pref)
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A reaction:
A particularly strong assertion of foundationalism, as it says that not only must the foundations exist, but also we must actually know them. This sounds false, as elementary knowledge then seems to require far too much sophistication.
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6944
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Demonstration does not rest on first principles of reason or sensation, but on freedom from actual doubt [Peirce]
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Full Idea:
It is a common idea that demonstration must rest on indubitable propositions, either first principles of a general nature, or first sensations; but actual demonstration is completely satisfactory if it starts from propositions free from all actual doubt.
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From:
Charles Sanders Peirce (The Fixation of Belief [1877], p.11)
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A reaction:
Another nice example of Peirce focusing on the practical business of thinking, rather than abstract theory. I agree with this approach, that explanation and proof do not aim at perfection and indubitability, but at what satisfies a critical mind.
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6945
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Once doubt ceases, there is no point in continuing to argue [Peirce]
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Full Idea:
Some people seem to love to argue a point after all the world is fully convinced of it. But no further advance can be made. When doubt ceases, mental action on the subject comes to an end; and, if it did go on, it would be without purpose.
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From:
Charles Sanders Peirce (The Fixation of Belief [1877], p.11)
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A reaction:
This is the way Peirce's pragmatism, which deals with how real thinking actually works (rather than abstract logic), deals with scepticism. However, there is a borderline where almost everyone is satisfied, but the very wise person remains sceptical.
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