TWO:��But who would want to destroy them?�� Dick wondered.It has been already shown how Extension, having become identified with matter, took on its mechanical qualities, and was conceived as a connected series of causes or modes of motion. The parallel found by Spinoza for this series in Thought is the chain of reasons and consequents forming a410 demonstrative argument; and here he is obviously following Aristotle, who although ostensibly distinguishing between formal and efficient causes, hopelessly confounds them in the second book of his Posterior Analytics.565 We are said to understand a thing when we bring it under a general rule, and also when we discover the mechanical agency which produces it. For instance, we may know that a particular man will die, either from the fact that all men are mortal, or from the fact that he has received a fatal wound. The general rule, however, is not the cause of what will happen, but only the cause of our knowing that it will happen; and knowledge of the rule by no means carries with it a knowledge of the efficient cause; as we see in the case of gravitation and other natural forces whose modus operandi is still a complete mystery. What deceived Aristotle was partly his false analysis of the syllogism, which he interpreted as the connexion of two terms by the interposition of a middle answering to the causal nexus of two phenomena; and partly his conception of the universe as a series of concentric spheres, through which movement is transmitted from without, thus combining the two ideas of notional comprehension and mechanical causation.