"That the sun will not rise tomorrow is no less intelligible a proposition, and implies no more contradiction, than the affirmation, that it will rise"
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David Hume’s assertion that “the sun will not rise tomorrow is no less intelligible a proposition, and implies no more contradiction, than the affirmation, that it will rise” delves into the nature of induction and the limits of human reasoning. He argues that our belief in the future resembling the past, such as the expectation that the sun will rise as it always has, is not grounded in logic or reason, but in habit and experience. When Hume claims that denying the sun’s rising is just as intelligible as affirming it, he challenges the assumption that continuity in nature is certain.
He is not directly suggesting that the sun's rising is unlikely, but rather emphasizing that the proposition "the sun will not rise tomorrow" does not contain a logical contradiction. For instance, it is not like saying "a square circle exists", which is self-contradictory. Both statements, the prediction of sunrise and the prediction of no sunrise, are possible within the framework of logic. What determines our expectations for tomorrow is the constant conjunction found in past experience: the sun has always risen, so we anticipate it will continue to do so. However, Hume warns that this assumption is not based on rational necessity; it is simply psychological conditioning resulting from repeated observation.
The implications of Hume’s argument are profound for philosophy and science. He draws a distinction between relations of ideas (necessary truths, like mathematics) and matters of fact (contingent truths based on experience). The expectation that natural laws will persist is a matter of fact, not a logical certainty. Thus, there is always the open possibility that the future might not resemble the past. No amount of evidence can logically guarantee that the sun will rise tomorrow; our confidence in such expectations rests on custom, not necessity. Hume’s insight reveals the fragility and uncertainty inherent in empirical knowledge, calling attention to the limits of what reason alone can assure.
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