I typically greet my cat, Wolfy, whenever I see him. He's the type of cat that would walk into a room and meow a couple times to inform us that he's around. So if he's saying hello or complaining, then I'd give him a greeting or ask him what's wrong. But that's the most that I would do.
As for my father... I can't say that he does the same thing. He will have a flat out conversation with the cat. Wolfy often looks confused (which he should be) and my father would rant about his day at work or future decisions. Granted, it helps my father get over things and come up with brilliant ideas. But to talk to a cat about it... It can look kind of crazy, but at least I understand where he's coming from.
So when I see other people talking to their pets, it can be understandable. Sometimes it's pure loneliness, or sometimes they just need to hear themselves think aloud, and that's the best way to do so without looking like a complete crazy person.
