"..all arguments concerning existence are founded on the relation of cause and effect; that our knowledge of that relation is derived entirely from experience; and all our experimental conclusions proceed upon the supposition that the future will be conformable to the past. .... Without the influence of custom, we should be entirely ignorant of every matter of fact beyond what is immediately present to the memory and senses."

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This can never become popular, and, indeed, has no occasion to be so; for fine-spun arguments in favour of useful truths make just as little impression on the public mind as the equally subtle objections brought against these truths. On the other hand, since both inevitably force themselves on every man who rises to the height of speculation, it becomes the manifest duty of the schools to enter upon a thorough investigation of the rights of speculative reason, and thus to prevent the scandal which metaphysical controversies are sure, sooner or later, to cause even to the masses.

— Immanuel Kant