When we take any one of the numerous examples of the working of this principle in the adult, and carefully analyze it, we can detect three distinct stages in the operation, before the effect is produced. The _first_ is the knowledge of some useful truth, present to the mind, and at the command of the will;--there is, _secondly_, an inference drawn from that truth, or portion of our knowledge, or the impression of an inference which was formerly drawn from it, and which, as we have seen in the infant, may remain long after the circumstance from which the lesson was derived has been forgotten;--and there is, _thirdly_, a special application of that inference or impression to our present circumstances. For example, in the case of the person leaving the house, and suddenly returning to provide himself with an umbrella, there is first the knowledge of a fact, that "the sky is lowering;" then there is an inference drawn from this fact, that "there will most probably be rain;" but the comfort--the whole benefit arising from this knowledge, and from this reasoning upon it,--depends on the third stage of the operation, which is therefore the most important of all, namely, the application of the inference, or lesson, to his present circumstances. A mere knowledge of the fact that the sky lowered, would have remained a barren and a useless truth in the mind, unless he had proceeded to draw the proper inference from it; and the inference itself, after it was drawn, would have done him no good, but must rather have added to his uneasiness, had he not proceeded to the third step of the operation, and applied the whole to the regulation of his conduct, in providing himself with an umbrella or a cloak. In like manner, in the supposed case of the mariner expecting a storm, there was first the knowledge of the fact, that the "sky was in a certain state." Now of this knowledge every person on board might have been in possession as well as the master himself, without the slightest benefit accruing to themselves or the ship, unless they had been trained, or enabled to draw the proper inference or lesson from it. The mere possession of the knowledge, therefore, would have been of no advantage. But the practised eye, and the previous experience of the master, enabled him to draw the inference, that "there will be a storm." Even this, however, would not have saved the ship and crew, without the third, and the most important step of all,--the application of that inference or lesson to their present condition. It was that which induced him to give the necessary orders to prepare for the storm, and thus to secure the safety both of the ship and of all on board.