Did you ever notice that, on that show, the salt shaker talked, the mailbox talked, the side-table drawer talked... but the eponymous Blue — no speakee. And for that matter, no one ever disciplines Blue for getting his (her?) paw-prints all over the carpet, house, walls, etc etc etc.
And what's up with Mickey Mouse? He keeps a pet that's a deaf-and-dumb member of the same species as one of his best friends...
LOL.
Now, as to Goofy: his species is the subject of some extended, enlightened debate in "The Body"/"Stand by Me," as I recall. "If Mickey was a mouse, Donald was a duck and Pluto a dog...what's Goofy?"
Dan