Latin scrupus is a rough, sharp stone; the diminutive scrupulus is the small one that gets in your sandal. Both figurative senses are ancient: a very small amount, codified as the apothecary weight of twenty grains, 1/24 of an ounce, 1.296 grams, three scruples to the drachma; and the mental discomfort, used by Cicero himself, the anxiety like a stone in the shoe. The moral sense, an ethical principle that inhibits action, is attested by the 15th century, and the apothecary symbol ℈ stood in every prescription beside the ounce ℥ and dram ℨ. Pharmacists, the joke goes, must have scruples: they literally dispensed them.
The scruple's pharmacy life was the era when the dose was the difference between the Pharmakon's two faces: a scruple too much opium in the treacle and the antidote became the poison, so the smallest weight carried the heaviest ethics. The prescription's whole moral economy ran on tiny stones, grains of barley for the grain weight, and the druggist who shorted the scruple poisoned the patient or cheated the price. The modern conscience, that pebble you cannot shake out, inherited the pharmacist's daily question: is the measure exact, and who checks the measurer?
The claim: scruple's double life proves morality was always metrology, the felt weight of a wrong action as precisely quantifiable as twenty grains, guilt as the scale reading off-spec, and the modern phrase without scruples describing, literally, someone whose pharmacist's balance has been disabled. Verdict: the Romans built the metaphor and this archive endorses it, with the standing question the pharmacopoeia wing always asks: who owns the scale. A scruple is a weight. Weights are calibrated by authorities. Your conscience, like your prescription, comes pre-measured. The pebble in the shoe was the only one you weighed yourself.
If morality is measured in apothecary weights, what is the modern dose of a scruple, and who is under-prescribing?