A maiore ad minus

In logic, a maiore ad minus describes a simple and obvious inference from a claim about a stronger entity, greater quantity, or general class to one about a weaker entity, smaller quantity, or specific member of that class:

• From general to particular ("What holds for all X also holds for one particular X") (essentially a less formal version of modus ponens, the best-known form of the classical syllogism and the one embodied in "All men are mortal. ...")
• From greater to smaller ("If a door is big enough for a person two meters high, then a shorter person may also come through"; "If a canister may store ten liters of petrol, then it may also store three liters of petrol.")
• From the whole to the part ("If the law permits a testator to revoke the entirety of a bequest by destroying or altering the document expressing it, then the law also permits a testator to revoke the portion of a bequest contained in a given portion of a document by destroying or altering that portion of the document.")
• From stronger to weaker ("If one may safely use a rope to tow a truck [in the American usage], one may also use it to tow a car.")

The reverse of this argument is a minore ad maius. Both of these arguments fall within the class of a fortiori arguments.