(n.) a person’s inner knowledge of right and wrong
Before we had a conscience, we had inwit—a Middle English-period word for a person’s inner knowledge of what is right and wrong.
The ‘wit’ in inwit is the same one we talk about today. Wit variously meant ‘reasoning’, ‘understanding’, ‘intellect’, or ‘the faculty of thought’ in Old English, and we still use it to mean ‘knowledge’ or ‘mental capacity’ today.
It’s from here that the more specified use of wit to mean ‘comic timing’ or ‘sense of humour’ developed in the 1500s, but the earlier more general meaning of wit still survives in English today. It is this wit, for instance, that you can be at the end of; that you keep about you when you need to be wary; that you can be out of when you lose your temper; and that you can have when you know how to do something correctly.
Back in Old English, wit was a verb too, equivalent ‘to know’ today; when we use the legalese expression to wit to mean ‘that is to say’ or ‘in this way’, we’re using the only surviving form of this verb that remains in use.
Inwit is quite literally ‘inner wit’. But while wit is an Old English word (you’ll find in it Beowulf, for instance), inwit isn’t recorded in written English until the Middle English period, and has been unearthed by the Oxford English Dictionary in documents probably written in the late 1100s. Given its roots, however, we can assume that it was probably in use in spoken English a little earlier than that written evidence might suggest—and so has probably been around in the language longer than the word that eventually replaced it.
Conscience was borrowed into English around the beginning of the thirteenth century. Although it likely found its way into our language via French, we could just have easily picked it up directly from Latin: conscienta was common knowledge in Latin, or an inner knowledge uniting all minds as to what was right and wrong. Etymologically, it comes from the Latin verb scire, meaning ‘to know’—which is also the origin of words like science, nescience and omniscience.
For a time, both words existed alongside one another in English, but alas inwit fell out of use in the 1500s. Quite why the one replaced the other is unclear, but given the Early Modern Period’s zealous preference for more classically-influenced words over bog-standard English one, it could be that inwit simply sounded too resolutely Anglo-Saxon to be maintained.
Whatever the case, it all but disappeared from the language in the sixteenth century as conscience became the more familiar and established term—at least, until James Joyce resurrected it from obscurity in Ulysses in 1922.