Philosophical razor

In philosophy, a razor is a principle or rule of thumb that allows one to eliminate (shave off) unlikely explanations for a phenomenon, or avoid unnecessary actions.

Examples
Razors include:
 * Alder's razor (also known as Newton's flaming laser sword): If something cannot be settled by experiment or observation, then it is not worthy of debate.
 * Einstein's razor: "The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience."  Often paraphrased as "make things as simple as possible, but no simpler."
 * Grice's razor (also known as Giume'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's 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 which require fewer unjustified assumptions are more likely to be correct; avoid unnecessary or improbable assumptions.
 * Popper's falsifiability principle: For a theory to be considered scientific, it must be falsifiable.
 * Sagan standard: Extraordinary claims require extraordinary evidence.