2. This doctrine, taken in conjunction with the known skepticism of its author on religious points, produced a considerable fermentation in the speculative world. The solution of the difficulty thus thrown before philosophers, was by no means obvious. It was vain to endeavour to find in experience any other property of a Cause, than a constant sequence of the effect. Yet it was equally vain to try to persuade men that they had no idea of Cause; or even to shake their belief in the cogency of the familiar arguments concerning the necessity of an original cause of all that is and happens. Accordingly these hostile and apparently irreconcilable doctrines,--the indispensable necessity of a cause of every event, and the impossibility of our knowing such a necessity,--were at last allowed to encamp side by side. Reid, Beattie, and others, formed one party, who showed how widely and constantly the idea of a cause pervades all the processes of the human mind: while another sect, including Brown, and apparently Stewart, maintained that this idea is always capable of being resolved into a constant sequence; and these latter reasoners tried to obviate the dangerous and shocking inferences which some persons might try to draw from their opinion, by declaring the {180} maxim that "Every event must have a cause," to be an instinctive law of belief, or a fundamental principle of the human mind[5\3]. [Note 5\3: Stewart's _Active Powers_, vol. i. p. 347. Browne's _Lectures_, vol. i. p. 115.] 3. While this series of discussions was going on in Britain, a great metaphysical genius in Germany was unravelling the perplexity in another way. Kant's speculations originated, as he informs us, in the trains of thought to which Hume's writings gave rise; and the _Kritik der Reinen Vernunft_, or _Examination of the Pure Reason_, was published in 1787, with the view of showing the true nature of our knowledge. Kant's solution of the difficulties just mentioned differs materially from that above stated. According to Brown[6\3], succession observed and cause inferred,--the memory of past conjunctions of events and the belief of similar future conjunctions,--are facts, independent, so far as we can discover, but inseparably combined by a law of our mental nature. According to Kant, causality is an inseparable condition of our experience: a connexion in events is requisite to our apprehending them _as_ events. Future occurrences must be connected by causation as the past have been, because we cannot think of past, present, and future, without such connexion. We cannot fix the mind upon occurrences, without including these occurrences in a series of causes and effects. The relation of Causation is a condition under which we think of events, as the relations of space are a condition under which we see objects. [Note 6\3: _Lectures_, vol. i. p. 114.]