substantially

In the 1260s, Thomas Aquinas was working through Aristotle's Categories in Paris, translating and commenting on the Greek philosopher's distinction between substance and accident. The Latin word he used constantly was substantia, from sub (under) and stare (to stand). What stands under appearances, Aquinas argued, is what truly and completely is. From this scholastic argument came the adjective substantialis, meaning belonging to the essence of a thing rather than to its surface qualities.

Old French inherited the adjective as substantiel by the thirteenth century and passed it to Middle English as substantial by the fourteenth. At first the English word kept its philosophical weight: a substantial form was a real form, not a mere appearance. But by 1400, writers were already using it to mean simply large or solid. The Paston Letters of the 1420s use substancyall to describe a reliable man, meaning someone with real standing in the community.

The adverb substantially appears in the fifteenth century, first in legal and religious texts. By the sixteenth century it meant for the most part or to a considerable degree, a semantic slide from metaphysics toward quantity. Shakespeare uses it in this diluted sense, as does Francis Bacon. The philosophical origin was not entirely forgotten: substantially still implies that something is real and not merely apparent, even when it simply means greatly.

The word survived every simplification of the seventeenth and eighteenth centuries because it filled a gap between mostly and completely. It suggests weight, solidity, and consequence without claiming absolute perfection. A substantially finished building is real and usable, even if the trim is missing. That precision, borrowed from Aquinas without anyone knowing it, made the adverb indispensable to legal writing, science, and politics.