The second way is based on the notion of efficient causation. In the observable world we discover an order of efficient causes, but no case is found, or ever could be found, of something efficiently causing itself. Such a thing would have to be prior to itself, which is impossible. Now it is impossible to go on for ever in a series of efficient causes. For in every ordered series of efficient causes the first member of the series causes the intermediate member or members, which in turn cause the final member. If you eliminate a cause you eliminate its effect, so there will not be final or intermediate members in the series unless there is a first member. But if the series goes on forever, then there will be no first efficient cause; and so there will be no final effect and no intermediate efficient cause, which is obviously false. Therefore it is necessary to posit some first efficient cause, to which everyone gives the name 'God'.1