Imperial units were built around the human body and everyday tasks

The argument

Proponents of the imperial system begin from where its units came from. A foot, a hand, a pace and a thumb-width are measures taken from the body, and the quantities they describe are the ones people actually handle: the height of a step, the width of a plank, the depth of water under a boat. On this account imperial units are not arbitrary survivals but the sediment of practical use, refined over centuries by the trades that depended on them, and that is why they sit so comfortably in ordinary speech and ordinary work. The second half of the case is arithmetical. Imperial units are built on numbers with many divisors, so they split cleanly in the ways a maker needs. A foot divides into halves, thirds, quarters and sixths without leaving a remainder, and the pound and the gallon divide the same way. Proponents argue that this matters precisely where measurement is done by hand rather than by calculator: a carpenter marking out a shelf, a cook halving a recipe or a builder dividing a run into equal bays can do the sum in their head, whereas a decimal scale divided in three gives a figure that must be rounded and then accumulates error. Taken together, the claim is that the imperial system is better adapted to the human scale at which most measuring is actually done. Its units are estimable without instruments, because the reference is the body of the person estimating; its subdivisions fall where craft work needs them; and its names carry meanings that have been understood for generations. Proponents conclude that a system suited to the hand and the eye is a better everyday tool than one suited to the page, even if the latter is tidier to write down.

Premises

Counter-arguments

Critics reply that the convenience is a habit rather than a property of the units. A system can be estimable only to the people raised in it, and the divisibility argument proves less than it seems: a decimal scale can be divided into thirds readily enough once the unit is chosen small enough, and the remainders that worry carpenters fall inside tolerances they already work within. They add that the human origin of the units is exactly the problem, since a foot taken from a body differed from place to place until it was fixed by statute, and what fixed it was an arbitrary definition of the kind imperial defenders object to in metric. On that reading imperial comfort is familiarity, and familiarity is not an argument for keeping a system that everyone else has to convert out of.

Rejecting the premises

[Rejecting P1] Estimating by the body works only for people trained on these units, and someone trained on metric estimates a metre or a centimetre just as readily, so the premise describes familiarity rather than a property of the system. [Rejecting P2] Divisibility is a feature of the number chosen rather than of the system: metric users pick a smaller unit when thirds matter, and hand trades already work to a tolerance that absorbs the remainder. [Rejecting P3] Much everyday measuring now happens through instruments, labels and devices that display whatever units they are set to, so the appeal to hand estimation covers a shrinking part of the practice. [Rejecting C] At most it follows that imperial units are convenient for certain manual tasks, not that the system as a whole is the better one.