The absolute validity of this method of argument and calculation will be yet more apparent to the reader when we pursue a step farther our analysis of reasoning generally as applied to practical matters, and consider it especially when it takes the form of a direct discussion with regard to causes and effects. In the strictest sense of the word it would plainly be quite impossible to specify fully the causes of even effects of the simplest kind. The motion, for instance, of a ball when a cricketer hits it, would, in any discussion of the game, be said to have been caused by {209} the cricketer; but the entire antecedents and conditions which have rendered this effect possible comprise not only all the incidents of the cricketer’s past training, but the history of cricket itself, and half the properties of matter. It would be impossible and useless to specify all these. When we say that anything is the cause of anything else, we are always selecting that cause out of an indefinite number, on which, for the purpose on hand, it is practically important that we should insist; and the cause on which it is important that we should insist for practical purposes will be found to be always one which, under the circumstances in view, may or may not be present,‡—which a careless person may neglect to introduce, or an ignorant person be persuaded to take away; whilst those other causes whose presence is assumed by all parties to the {210} discussion, and which no one proposes to take away, or which no one is able to take away, or whose number, if they were mentioned, would make all discussion impossible, are passed over in silence, for there is no need to mention them. Thus we all know that when a house is burnt to the ground the causes of the phenomenon comprise the inflammable nature of timber, and indeed the whole chemistry of combustion; but if an insurance office is disputing the owner’s claim to compensation on the ground that the owner set a light to it purposely, whilst the owner maintains that the scullery-maid set it alight by accident whilst reading in bed a novel of Belgravian life, the only causes that will be put forward by the litigants will, let us say, be a candle alleged by the owner to have ignited the scullery-maid’s pillow-case accidentally, and on the other hand a match which is alleged by the agent of the insurance office to have been applied by the owner to the drawing-room curtains intentionally. Or again, let us take the case of a ship’s chronometer. The reliability of a chronometer, any practical man will tell us if we ask him about the matter, depends on the balance and the escapement. It is the perfect “compensation” of the former and what is called the “detachment” of the latter that differentiates the chronometer from the ordinary lever watch; and these are rightly said to be the causes of the chronometer’s superiority as a time-keeper. But a balance and escapement of themselves will not keep time at all.