In the whole conduct of the understanding there is nothing of more moment than to know when and where and how far to give assent,and possibly there is nothing harder.It is very easily said,and nobody questions it,that giving and withholding our assent,and the degrees of it,should be regulated by the evidence which things carry with them;and yet we see men are not the better for this rule;some firmly embrace doctrines upon slight grounds,some upon no grounds,and some contrary to appearance.
Some admit of certainty and are not to be moved in what they hold;others waver in everything,and there want not those that reject all as uncertain.
What then shall a novice,an enquirer,a stranger do in the case?I answer,use his eyes.
There is a correspondence in things,and agreement and disagreement in ideas,discernible in very different degrees,and there are eyes in men to see them if they please,only their eyes may be dimmed or dazzled and the discerning sight in them impaired or lost.Interest and passion dazzle;the custom of arguing on any side even against our persuasions,dims the understanding and makes it by degrees lose the faculty of discerning clearly between truth and falsehood,and so of adhering to the right side.It is not safe to play with error and dress it up to ourselves or others in the shape of truth.The mind by degrees loses its natural relish of real solid truth,is reconciled insensibly to anything that can but be dressed up into any faint appearance of it;and if the fancy be allowed the place of judgement at first in sport,it afterwards comes by use to usurp it,and what is recommended by this flatterer (that studies but to please)is received for good.There are so many ways of fallacy,such arts of giving colors,appearances and resemblance's by this court-dresser,the fancy,that he who is not wary to admit nothing but truth itself,very careful not to make his mind subservient to anything else,cannot but be caught.He that has a mind to believe has half assented already;and he that by often arguing against his own sense imposes falsehoods on others is not far from believing himself.This takes away the great distance there is betwixt truth and falsehood;it brings them almost together and makes it no great odds,in things that approach so near,which you take;and when things are brought to that pass,passion or interest,etc.,easily and without being perceived determine which shall be the right.