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CAUSATION AND EVOLUTION.
all co-operated indeed to bring about the jar; but they have got their peculiar functions of their own. So long the jar is there, clay is there too. The actual existence of the jar cannot come to be as such if you extract out clay from it. But after the production of the jar, if the manufacturer or the millstone is separated from the jar, it is not in the least affected. Again the function of the manufacturer is not the same with that of the mill-stone or the lever or clay even. It is clay that is cast into the mould and moulded into the form of the jar, and it is for this reason that clay is named as the substantial cause and that by means of which the effect already existing impercep tibly in the substantial cause is brought about or developed into a perceptible form is the efficient or determining cause. That without which nothing can there be, that which invariably precedes something else which is but an effect, is the true nature of the cause. When we see that the jar cannot come into existence either without the manufacturer or without the mill-stone, and the lever, it follows a priori therefore
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Nature and functions of the two causes ex
plained.
