shown at length that this favourite conception is inadmissible. It may be remarked, that authors usually have recourse to it just when their insight is becoming less clear, and this accounts for the frequency of its use. Nay, it is precisely when a writer comes to the end of his conceptions, that the word reciprocity presents itself more readily than any other; it may, in fact, be looked upon as a kind of alarm-gun, denoting that the author has got out of his depth. It is also worthy of remark, that the word Wechselwirklung, literally reciprocal action — or, as we have preferred translating it, reciprocity — is only found in the German language, and that there is no precise equivalent for it in daily use in any other tongue.
From the law of causality spring two corollaries which, in virtue of this origin, are accredited as cognitions à priori, therefore as unquestionable and without exception. They are, the law of inertia and that of permanence of substance. The first of these laws avers, that every state in which a body can possibly be — consequently that of repose as well as that of any kind of movement — must last for ever with out change, diminution, or augmentation, unless some cause supervenes to alter or annul it. But the other law, by which the eternity of Matter is affirmed, results from the fact, that the law of causality is exclusively applicable to states of bodies, such as repose, movement, form, and quality, since it presides over their temporal passing in or out of being; but that it is by no means applicable to the existence of that which endures these states, and is called Substance, in order precisely to express its exemption from all arising and perishing. 'Substance is permanent 'means, that it can neither pass into, nor out of being: so that its quantity existing in the universe can neither be increased nor diminished. That we know this à priori, is proved by the consciousness of unassailable certainty with which, when we see a body disappear — whether it be by conjuring, by minute subdivision,
