A few days ago, my iTunes brought me Thomas Tallis’s magificent motet Spem in alium (ca. 1570), as performed by the Choir of King’s College, Cambridge — causing me to stop what I was doing and just listen to this extraordinary 40-part masterpiece (eight choirs of five singers each) for 11 minutes. I’ve never experienced a live performance of it, much less a performance with the singers arrayed in a horseshoe around the listeners. (Understandably, it’s not often performed, because of the extraordinary demands it makes on the singers.)
I bring it up here because of the name Spem in alium — the first three words of the Latin text, which begins
Spem in alium nunquam habui praeter in te ‘I have never put (my) hope in any other but in You, I have never had hope in another beyond/besides/except in You’
That is, spem in alium ‘hope in another’. Without the context you can’t tell that this phrase is not in fact a constituent in Latin; it’s not spem in alium ‘hope in another’ functioning as a NP, but rather the sequence of the NP spem ‘hope (acc.)’ and the PP in alium ‘in another’, both functioning as complements of the perfect verb habui ‘I have had’. So it’s a part of a VP constituent but not a constituent on its own.
A while ago, Geoff Pullum collected examples of non-constituent book titles, for example Andrew Holleran’s Dancer From the Dance (like Spem in alium, a non-constituent of the form NP + PP); see Language Log postings here and here. He observed that such titles seem to be pretty rare in English. I’d imagine that the practice of referring to Latin texts by their first few words will yield many more Latin examples, especially given the famously free word order of Latin.