Yeoman's Rules of Logic.

Chesterton's Fence:

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."

Chesterton, The Thing. 

Hanlon's Razor

Never attribute to malice that which can be adequately explained by stupidity.

Occam's razor

Pluralitas non est ponenda sine necessitate (plurality should not be posited without necessity.).

Yeoman's Gate:

Before you go through a gate to get to the other side of a fence, completely figure out, to the extent you can, where the path goes.

Yeoman's Gatekeeper

If somebody is holding a fence open, urging you to go through, or keeping it closed, trying to bar you from doing so, ask what interest he has in either action.

Yeoman's Self Centered Razor

Something is not true, or false, because that answer fits your deeply held metaphysical or philosophical beliefs.  Nor is something true, or false, because that answer comports with your own self-interest.