The first the capacity to learn. If one cannot learn, how can it be sentient? The second is the capacity to reason. A dumb animal cannot reason, setting it apart from those that can reason between the choices provided it. And the third principle is the ability to self-sacrifice. If one can override the rules of fight and flight to sacrifice themselves for a cause, a friend, a loved one, that is in itself the highest form of sentient life.
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar - B5
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar - B5
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar-B5