History and sources

Twenty-first on this list is il trattato, given here as a treaty because the sentence beside it is about a signature in a railway station. The word does a second job that English hands to a different noun altogether. Un trattato is also a treatise: Leonardo’s Trattato della pittura is a book and not a pact, and un trattato di diritto civile is the fat volume a student carries about. English keeps the two apart, and the split is nothing but a matter of which door each word came through. « Treaty » and « treatise » both go back to Latin tractare, to handle, to deal with a thing — and dealing with a matter is exactly what two states do at a table and what an author does over four hundred pages. English took one Anglo-Norman form for the agreement and another for the book, and has kept them a syllable apart ever since. Italian never separated them, so the sentence has to. If it is signed, it is a treaty; if it is read, it is a treatise.