Outward corporeal objects that constantly importune our senses and captivate our appetites fail not to fill our heads with lively and lasting ideas of that kind.Here the mind needs not be set upon getting greater store;they offer themselves fast enough and are usually entertained in such plenty and lodged so carefully,that the mind wants room or attention for others that it has more use and need of.To fit the understanding therefore for such reasoning as I have been above speaking of,care should be taken to fill it with moral and more abstract ideas;for these not offering themselves to the senses,but being to be framed to the understanding,people are generally so neglectful of a faculty they are apt to think wants nothing,that I fear most men's minds are more unfurnished with such ideas than is imagined.They often use the words,and how can they be suspected to want the ideas?What I have said in the third book of my essay will excuse me from any other answer to this question.But to convince people of what moment it is to their understandings to be furnished with such abstract ideas steady and settled in it,give me leave to ask how anyone shall be able to know whether he be obliged to be just,if he has not established ideas in his mind of obligation and of justice,since knowledge consists in nothing but the perceived agreement or disagreement of those ideas;and so of all others the like which concern our lives and manners.
And if men do find a difficulty to see the agreement or disagreement of two angles which lie before their eyes,unalterable in a diagram,how utterly impossible will it be to perceive it in ideas that have no other sensible objects to represent them to the mind but sounds,with which they have no manner of conformity and therefore had need to be clearly settled in the mind themselves if we would make any clear judgment about them.This,therefore,is one of the first things the mind should be employed about in the right conduct of the understanding,without which it is impossible it should be capable of reasoning right about those matters.But in these and all other ideas care must be taken that they harbor no inconsistencies,and that they have a real existence where real existence is supposed and are not mere chimeras with a supposed existence.