"Our grandfather is Italian but for the last four years he has been living in America."
Translation:Наш дедушка — итальянец, но последние четыре года он живёт в Америке.
Thanks. "Our grandpa is Italian, and has been living in the U.S. for the last 4 years". is a perfectly good sentence in English, but of course it doesn't contain the feel of contrast that 'but' or 'however' carry, which is what the Russian sentence contains. I need to review the Russian usage since I had a wrong-headed notion that 'a' is used for contrast.
"contrast" is not the same as contradiction. Maybe, "juxtaposition" is a better word. Imagine two frames holding different pictures. "This picture here shows my grandpa, he's Italian; and in this picture you can see my grandma, she's a Swede". You see the "comparison" of two different things side by side, conveniently aided by a guy telling you the story.