First of all, I’m not anything like a Latin scholar. I took several years of Ancient Greek in college, but never Latin. However, I’ve been reading the most wonderful book about language in general called The Power of Babel: A Natural History of Language by John McWhorter, and from that I’ve been learning some things about how languages work. So when a buddy of mine emailed me a question about the Latin text of a song, wanting to know why it’s spelling kept changing so much, I was able to answer him with just a little bit of on-line research.
Lux aeterna luceat eis, Domine, cum sanctis tuis in aeternum, quia pius es. Requiem aeternam dona eis, Domine; et lux perpetua luceat eis,
“May everlasting light shine upon them, O Lord, with thy saints in eternity, for thou art merciful. Grant them eternal rest, O Lord, and may everlasting light shine upon them.”
In this text there are these words: aeternum and aeternam.
What’s the difference(s)?
Here is my answer:
I’m not all that good at Latin, but I think I know enough to answer this particular question.
The word Aeternus is the Latin adjective that means eternal, or without end. In fact, the word eternal in English is a direct descendant from aeternus. If you say them both fast, they sound similar.
As to why the word aeternus is spelled three different ways (aeterna, aeternum, and aeternam) in the same paragraph, that takes a bit to explain.
See, in many languages, like English, the way you tell what the words are doing in a sentence is by their order. Usually the order is subject, verb, object, although some languages do their order differently.
Take the sentence: The girl ate a sandwich.
The subject (the person doing the action) is the girl. The verb (the action) is ate, and the object (the thing being acted upon, in this case, being ate) is the sandwich. When you read this sentence you know it is about a girl, eating a sandwich.
But what happens if you rearrange the word order? What if you write: A sandwich ate the girl.
Uh, oh. Those are the same words, but it means something completely different from the first sentence, at least in English.
As it happens there are some other languages, like Latin and Greek, that solve this word order problem differently. What Latin and Greek do is add a suffix to the end of the words so the listener (or reader) knows what is being done to who, regardless of the word order. So in Latin you could write:
And they would all mean the same thing (a girl eating a sandwich) as long as you used the proper suffixes for each of the words. In each case girl would get the subject suffix, ate would get the subject suffix as well (so you know its the girl doing the action), and sandwich would get the object suffix.
This is a neat trick for a language. Among other things it makes it easy to write long epic poems because the author is free of the limitations of word order when writing. They can rearrange the words to work best (in terms of rhyme and meter) without worrying about word order. But its also a bit of a pain for non-native speakers because you have to memorize all the proper suffixes so you can follow what is going on.
The pretty girl owns a car
You would know that the word pretty applies to the girl. Change the sentence to:
The girl owns a pretty car
And now its the car that is pretty, not the girl. But again, like we saw before, in Latin and Greek you can rearrange the word order all you want, as long as the proper suffix is placed on the adjective so that the word pretty matches the ending of its subject.
One more thing, before we dig into the sentence. Many times in a language, an adjective will be so handy that eventually it starts to get used as a noun. Most languages have a way of taking adjectives and converting them into nouns for just this reason. Usually by changing their spelling. As it happens English does this the same way Latin and Greek do, by adding a suffix to the end of the adjective. Thus the adjective happy, because the noun happiness, by putting –ness on the end. In the same way forgetful becomes forgetfulness.
As you can probably guess, Latin and Greek not only adds a suffix, but they also change the spelling of it to indicate what they are modifying. Roughly the same thing as English, just slightly more complicated.
So now, lets go back to that Latin sentence.
Lux aeterna luceat eis, Domine, cum sanctis tuis in aeternum, quia pius es. Requiem aeternam dona eis, Domine; et lux perpetua luceat eis.
The first use of Aeternus comes at the beginning with aeterna. Here its an adjective modifying the noun Lux (or light) which also happens to be the subject of the sentence, hence the –a ending. The second time the word shows up as aeternum with the –um suffix. This suffix tells us the word is now a noun. So, instead of the adjective, eternal, it is the noun meaning eternalness. The third time the word shows up, aeternam, its back to the adjective form, only this time its modifying the object of the sentence instead of the subject like above. In this case its modifying the word requiem, meaning rest. Thus the –am ending.
So the same adjective, used three different ways. Once modifying the subject, once as a noun, and once modifying the object.
There’s more to it than this, but I think this gives you a good idea of why the word is spelled so differently.