In addition to having meaningful interactions with others, i would add consciousness also requires meaningful interaction with its-self.
What is 'meaninful' also comes down to language, which, personally, leads me back to the idea that consciousness is essentially a linguistic product/phenomenon. Duck-typed.
And at the end of the day, if you enjoy spending time asking "is this thing really x" where x lies on a vector you can't even begin measure, I got this deal on a bridge you can get in on, real cheap...
For most people, being conscious is proved by things like mourning dead companions, like caring for your babies and showing distress if they are missing/hurt, like being friendly and playful. That's why most people feel that certain animals they interact with more or have seen on TV are conscious (dogs, cats, elephants, whales, chimps and other primates), but that other animals are not (insects, rats, fish). Note that I am not saying that rats are objectively less conscious than dogs by these criteria, just that this is what many people base their beliefs on, and that it of course depends on their knowledge as well.
> Every other human, whose brain you have no ability to peer into, could be an unconscious yet sufficiently advanced computer, or a machine built to make the exact motions, words, decisions, etc., that you perceive, and you wouldn’t be able to tell the difference.
Makes no sense, in this conception of consciousness, any more than you can fake intelligence. Basically consciousness might just be what we call the inner workings of the mind of a sufficiently advanced agent, one capable at least of meaningfully interacting with other agents around it.
I'm not saying this is the correct theory, but it's a perfectly valid theory of consciousness, just like all the others.