The real purpose of his voyage was/were the souvenirs he got.
Do I use a singular verb because of purpose or a plural verb because of souvenirs?
I hope that you can help me. Thanks a lot!
Generally we would rephrase such a sentence. What was the purpose? Not souvenirs but "getting" or "to get" souvenirs.
Thus we might write: "The real purpose of his voyage was to get souvenirs."