As soon as a thought has found words it no longer exists in us or is serious in its deepest sense. When it begins to exist for others it ceases to live in us; just as a child frees itself from its mother when it comes into existence. The poet has also said: "Ihr müsst mich nicht durch Widerspruch verwirren! _Sobald man spricht, beginnt man schon zu irren_." The pen is to thought what the stick is to walking, but one walks most easily without a stick, and thinks most perfectly when no pen is at hand. It is only when a man begins to get old that he likes to make use of a stick and his pen. A hypothesis that has once gained a position in the mind, or been born in it, leads a life resembling that of an organism, in so far as it receives from the outer world matter only that is advantageous and homogeneous to it; on the other hand, matter that is harmful and heterogeneous to it is either rejected, or if it must be received, cast off again entirely. Abstract and indefinite terms should be employed in satire only as they are in algebra, in place of concrete and specified quantities. Moreover, it should be used as sparingly as the dissecting knife on the body of a living man. At the risk of forfeiting his life it is an unsafe experiment. For a work to become _immortal_ it must possess so many excellences that it will not be easy to find a man who understands and values them _all_; so that there will be in all ages men who recognise and appreciate some of these excellences; by this means the credit of the work will be retained throughout the long course of centuries and ever-changing interests, for, as it is appreciated first in this sense, then in that, the interest is never exhausted. An author like this, in other words, an author who has a claim to live on in posterity, can only be a man who seeks in vain his like among his contemporaries over the wide world, his marked distinction making him a striking contrast to every one else. Even if he existed through several generations, like the wandering Jew, he would still occupy the same position; in short, he would be, as Ariosto has put it, _lo fece natura, e poi ruppe lo stampo_. If this were not so, one would not be able to understand why his thoughts should not perish like those of other men.