Finally, one of the essential qualities of the legislator is to show discretion in changing existing laws, and for this purpose he should be immune from the passions of men or at all events complete master of those which beset him. For law has no real authority unless it is ancient. Where a law is merely a custom which has become law, it is invested with considerable authority from the first, because it gains strength by the antiquity of the original custom. When on the other hand a law is not an old custom but runs counter to custom, then, before it can have any authority, it must grow old and become a custom itself.
In both cases it is on its antiquity that the law must depend for its strength. The law is like a tree, at first it is a tender sapling, then it grows up, its bark hardens, and its roots go deep into the ground and cling to the rock.
We ought to consider carefully before we venture to replace the forest tree by the young sapling. "Most legislators," said Usbek to Rhédi,[A] "have been men of limited abilities, owing their position to a stroke of fortune, and consulting nothing but their own whims and prejudices. They have often abolished established laws quite unnecessarily, and plunged nations into the chaos that is inseparable from change. It is true that, owing to some odd chance arising out of the nature rather than out of the intelligence of mankind, it is sometimes necessary to alter laws, but the case is very rare and when it does arise it should be handled with a reverent touch. When it is a question of changing the law, much ceremony should be observed, and many precautions taken, in order that the people may be naturally persuaded that laws are sacred things, and that many formalities must precede any attempt to alter them."
In this passage, as so often elsewhere, Montesquieu is quite Aristotelian, for Aristotle wrote: "It is evident that at times certain laws must be changed, but this requires great circumspection for, when there is little to be gained thereby, inasmuch as it is dangerous that citizens should be accustomed to find it easy to change the law, it is better to leave a few errors in our magisterial and legislative arrangements than to accustom the people to constant change. The disadvantage of having constant changes in the law is greater than any risk that we run of contracting a habit of disobedience to the law." For the law assuredly will be disobeyed, if we regard it as ephemeral, unstable, and always on the point of being changed.