an impression on several senses at once, it should be brought into contact with several, though with the limitations imposed in the seventh Principle of chap. viii.
7. For this there are three cogent reasons. Firstly, the commencement of knowledge must always come from the senses (for the understanding possesses nothing that it has not first derived from the senses). Surely, then, the beginning of wisdom should consist, not in the mere learning the names of things, but in the actual perception of the things themselves! It is when the thing has been grasped by the senses that language should fulfil its function of explaining it still further.
8. Secondly, the truth and certainty of science depend more on the witness of the senses than on anything else. For things impress themselves directly on the senses, but on the understanding only mediately and through the senses. This is evident from the fact that belief is at once accorded to knowledge derived from the senses, while an appeal is always made to them from a priori reasoning and from the testimony of others. We do not trust a conclusion derived from reasoning unless it can be verified by a display of examples (the trustworthiness of which depends on sensuous perception). No one could have such confidence in the testimony of another person as to disbelieve the experience of his own senses. Science, then, increases in certainty in proportion as it depends on sensuous perception. It follows, therefore, that if we wish to implant a true and certain knowledge of things in our pupils, we must take especial care that everything be learned by means of actual observation and sensuous perception.
9. Thirdly, since the senses are the most trusty servants of the memory, this method of sensuous perception, if universally applied, will lead to the permanent retention of knowledge that has once been acquired. For instance, if I have once tasted sugar, seen a camel, heard a nightingale sing, or been in Rome, and have on each occasion attentively impressed the fact on my memory, the incidents will
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