To definitively know whether someone is or isn’t conscious would require the ability to study their inner workings in great detail. Obviously we don’t have that ability in most situations, and yet we still come to the conclusion that most of the people around us are conscious. Similarly the only way to definitively know whether this chair is made of wood is to break it apart and see, otherwise it could be made of something else very cleverly disguised as wood. Despite that we have justifiable confidence in our judgment that it is made of wood, based only on the external properties of the chair, because a chair with the right external properties is likely to be made of wood even though the possibility of a fake exists. Likewise, we can make reliable judgments about whether someone or something is conscious based on their behavior (and species), even though these factors aren’t directly responsible for consciousness. (This is to refute the claim that we are behaviorists if we make judgments about consciousness on the basis of behavior.)
With that in mind let’s exercise our understanding of consciousness by applying it to a fictional example, R2-D2. Obviously it is quite reasonable to treat as unconscious all present day machines, since none have been designed to be conscious or have ever displayed any signs of developing consciousness on their own. R2-D2, however, exists in universe where it is quite clear that machines can be conscious. His companion, C-3PO, is almost certainly conscious. But why is it reasonable to say that C-3PO is conscious when no modern machine is? Well, C-3PO acts as if he were conscious, meaning that he creates the impression, through language, that he has a point of view through which the universe is understood, as well as a sense of self. Certainly it could all be an elaborate deception, but then again so could the behavior of the biological people we meet in real life. Thus it is reasonable to grant C-3PO the benefit of the doubt, and assume that he is conscious.
Unfortunately for our analysis R2-D2 cannot speak in a way we can understand, although he seems to be able to understand us. In that respect he is more like Chewbacca than he is like C-3PO. And Chewbacca certainly appears to be conscious. One reason to believe that Chewbacca is conscious derives from a design perspective and the knowledge that he is an intelligent, evolved, biological being. Let us put that aside for later. Even without resorting to a design perspective we still have good reason to believe that Chewbacca is conscious. Chewbacca expresses fear, anger (at losing to C-3PO), and discomfort. All of these basically self-centered emotions imply the existence of a self and a perspective on the world for which things can go better or worse. It is true that R2-D2 also expresses emotions, but they are usually of a different nature. R2-D2’s emotions usually revolve around what is happening to other people, as if they are comments about the situation. It is true that R2-D2 does express pain at one point, but he rarely expresses fear (often he completely ignores blaster fire). Although R2-D2’s emotions could be an expression of a basically stoic consciousness it is equally possible to attribute them to simply an emulation of real emotion, just as such emotions are added to some modern virtual creatures.
R2-D2 then is a kind of borderline case. There is no compelling reason to declare him conscious or unconscious. To settle the issue we must adopt the design perspective, where we attempt to guess at the internal workings of the person or thing in question based on the historical chain of events that led to their creation. When it comes to biological creatures considering their design means considering that they evolved. If the creature is basically an individual (and not, for example, part of a hive), then it is reasonable to suppose that it has a point of view if it has more than rudimentary intelligence, because a point of view (and a sense of self) is an evolutionarily simple way of structuring that intelligence so that it serves the survival needs of the individual. When considering artificial beings we need to consider why they were designed. Let’s first consider C-3PO. Before the prequels (which I will ignore) rewrote C-3PO’s history it was assumed that he was one of many droids designed to act as translators. And that role of translator requires the droid to be as much like a person as possible, in order to act as the best possible intermediary between two parties that cannot directly communicate. And so it isn’t unreasonable to suppose that C-3PO’s designers gave his type of droid consciousness in order to achieve that goal. R2-D2 however is an astromech, meaning that he is designed basically to function as an additional computer and to perform the occasional repair. From a design standpoint there is simply no need to make an astromech conscious. It is also telling that R2-D2’s designers decided not to include the capability to create human speech sounds even though he is built with the ability to create beeps and clearly can communicate in text when plugged into a spaceship. Leaving out speech would be almost a crime if R2-D2 was conscious, but if he is in fact lacking in consciousness it actually is an aid to the design; the whistles and beeps allow R2-D2 to create the appearance of having actual emotions, and adding speech would defeat that since it would quickly reveal R2-D2 as lacking any kind of consciousness. So, given that R2-D2 doesn’t display any behavior that would lead us to believe that he is conscious, considering the matter from the design perspective leads to the conclusion that R2-D2 lacks consciousness even though other droids in the Star Wars universe may possess it.