Here's the thing. You said a "submarine is a boat." Is it in the same family? Yes. No one's arguing that. As someone who is a scientist who studies boats, I am telling you, specifically, in science, no one calls submarines boats. If you want to be "specific" like you said, then you shouldn't either. They're not the same thing. If you're saying "boat family" you're referring to the naval grouping of Boats, which includes things from dinghys to warships to yachts. So your reasoning for calling a submarine a boat is because random people "call the underwater ones boats?" Let's get skiffs and canoes in there, then, too. Also, calling a road fairing vehicle a hatchback or a car? It's not one or the other, that's not how vehicles work. They're both. A submarine is a submarine and a member of the boat family. But that's not what you said. You said a submarine is a boat, which is not true unless you're okay with calling all members of the boat family boats, which means you'd call pontoons, barges, and other sea fairing vehicles boats, too. Which you said you don't. It's okay to just admit you're wrong, you know?