Philosophical razor

In philosophy, a razor is a principle or rule of thumb that allows one to eliminate unlikely explanations for a phenomenon, or avoid unnecessary actions. Common examples include:

Alder's razor : If something cannot be settled by experiment or observation, then it is not worthy of debate.
Grice's razor : As a principle of parsimony, conversational implicatures are to be preferred over semantic context for linguistic explanations.
Hanlon's razor: Never attribute to malice that which can be adequately explained by stupidity.
Hitchens' razor: That which can be asserted without evidence can be dismissed without evidence.
Hume's guillotine: What ought to be cannot be deduced from what is; prescriptive claims cannot be derived solely from descriptive claims, and must depend on other prescriptions. "If the cause, assigned for any effect, be not sufficient to produce it, we must either reject that cause, or add to it such qualities as will give it a just proportion to the effect."
Occam's razor: Explanations that require fewer unjustified assumptions are more likely to be correct; avoid unnecessary or improbable assumptions.
Popper's falsification criterion of demarcation: For a theory to be considered scientific, it must be falsifiable.
Sagan standard: Positive claims require positive evidence, extraordinary claims require extraordinary evidence.