I encountered the notion of “Chesterton’s Fence” this morning via Ozy Frantz.

In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, “I don’t see the use of this; let us clear it away.” To which the more intelligent type of reformer will do well to answer: “If you don’t see the use of it, I certainly won’t let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.”

This paradox rests on the most elementary common sense. The gate or fence did not grow there. It was not set up by somnambulists who built it in their sleep. It is highly improbable that it was put there by escaped lunatics who were for some reason loose in the street. Some person had some reason for thinking it would be a good thing for somebody. And until we know what the reason was, we really cannot judge whether the reason was reasonable. It is extremely probable that we have overlooked some whole aspect of the question, if something set up by human beings like ourselves seems to be entirely meaningless and mysterious.

There are reformers who get over this difficulty by assuming that all their fathers were fools; but if that be so, we can only say that folly appears to be a hereditary disease. But the truth is that nobody has any business to destroy a social institution until he has really seen it as an historical institution. If he knows how it arose, and what purposes it was supposed to serve, he may really be able to say that they were bad purposes, or that they have since become bad purposes, or that they are purposes which are no longer served. But if he simply stares at the thing as a senseless monstrosity that has somehow sprung up in his path, it is he and not the traditionalist who is suffering from an illusion.

I would tend to agree with the quote in its original social context as a dampener on progressive change. I think most fences we’ve put up are probably silly, but I think it’s worth investigating which ones those actually are before we tear them down (and then, pass me the err. whatever tool it is you use to dismantle a fence. Lets go with “hammer”).

But reading it I recognised a very different scenario in it: What happens pretty much the vast majority of time when a programmer encounters new code. The code inevitably has special cases in it which accrued over time to handle a variety of situations. As a result the code may be quite ugly in places. The temptation is of course to rip it out, and replace it with something clean and pure and much more easily comprehensible to you, without all this cruft and special cases.

But perhaps you should first ask why is it there in the first place? And what was it intended to keep out?