text: You will never understand this unless you have investigated the actual standard by which such conditions are relatively rated. As leaves cannot flourish by their own efforts, but need a branch to which they may cling and from which they may draw sap, so your precepts, when taken alone, wither away; they must be grafted upon a school of philosophy. Moreover, those who do away with doctrines do not understand that these doctrines are proved by the very arguments through which they seem to disprove them. For what are these men saying? They are saying that precepts are sufficient to develop life, and that the doctrines of wisdom (in other words, dogmas) are superfluous. And yet this very utterance of theirs is a doctrine just as if I should now remark that one must dispense with precepts on the ground that they are superfluous, that one must make use of doctrines, and that our studies should be directed solely towards this end; thus, by my very statement that precepts should not be taken seriously, I should be uttering a precept. There are certain matters in philosophy which need admonition; there are others which need proof, and a great deal of proof, too, because they are complicated and can scarcely be made clear with the greatest care and the greatest dialectic skill. If proofs are necessary, so are doctrines; for doctrines deduce the truth by reasoning. Some matters are clear, and others are vague: those which the senses and the memory can embrace are clear; those which are outside their scope are vague.