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300 they lose their strength and splendour, and fade at last in total evanescence.

The systems of learning therefore must be sometimes reviewed, complications analyzed into principles, and knowledge disentangled from opinion. It is not always possible, without a close inspection, to separate the genuine shoots of consequential reasoning, which grow out of some radical postulate, from the branches which art has engrafted on it. The accidental prescriptions of authority, when time has procured them veneration, are often confounded with the laws of nature, and those rules are supposed coëval with reason, of which the first rise cannot be discovered.

Criticism has sometimes permitted fancy to dictate the laws by which fancy ought to be restrained, and fallacy to perplex the principles by which fallacy is to be detected; her superintendence of others has betrayed her to negligence of herself; and, like the ancient Scythians, by extending her conquests over distant regions, she has left her throne vacant to her slaves.

Among the laws of which the desire of extending authority, or ardour of promoting knowledge, has prompted the prescription, all which writers have received, had not the same original right to our regard. Some are to be considered as fundamental and indispensable, others only as useful and convenient; some as dictated by reason and necessity, others as enacted by despotick antiquity; some as invincibly supported by their conformity to the order of nature and operations of the intellect; others as formed by accident, or instituted by example, and therefore always liable to dispute and alteration.