"Most students have no worthy exercise for their heads, and therefore languish and stupefy upon bad translations, which lose them both time and money. Appearances alone rule them, and they care not what they know, but what they are thought to know by a senseless multitude.--There are four principal stumbling-blocks in the way of arriving at knowledge--authority, habit, appearances as they present themselves to the vulgar eye, and concealment of ignorance combined with ostentation of knowledge.--Even if the first three could be got over by some great effort of reason, the fourth remains ready.--Men presume to teach before they have learnt, and fall into so many errors, that the idle think themselves happy in comparison; and hence both in science and in common life we see a thousand falsehoods for one truth.--And this being the case, we must not stick to what we hear and read, but must examine most strictly the opinions of our ancestors, that we may add what is lacking, and correct what is erroneous, but with all modesty and allowance.--We must, with all our strength, prefer reason to custom, and the opinions of the wise and good to the perceptions of the vulgar: and we must not use the triple argument; that is to say, this has been laid down, this has been usual, this has been common, therefore it is to be held by. For the very opposite conclusion does much better follow from the premises. And though the whole world be possessed by these causes of error, let us freely hear opinions contrary to established usage."