A fundamental question of our experience of the world, yet one finds it a challenge to distinguish between a person, and a human-being (a representation of the human species -homo-sapiens). The concepts are very simple; they are non-identical and the both concepts can be approached differently. The concept of a person can be approached in many ways. Why, for instance must the term person be adapted to that of a human species?
It makes sense to adapt the term person to that of other things, for example, there could be a person, who had the same physical appearance as your brother (of the same height, weight, skin tone, facial features and so on) but if one was to cut him open the internal biology would be completely different. Surely, they would still be a person, but biologically not a human being. It would not be fair to say; that such things do not exists. It is enough to suggest that such life forms are comprehendible, but lack the human biology.
This is providing that the concept of a person is not stretched too far, for example attempting to address an envelope as a person is not exactly adequate. Otherwise, the concept becomes meaningless or pointless. Usually when we define a person, we tend to do so because they have self-awareness and self-consciousness. In addition, another way of identifying the concept of a person (or not in this case) is being able to conceive the idea of a human being that is not a person. For example, someone in a coma depending on a life support machine can be certainly considered a human being, but the person is no longer there.
Surely in order to be a person, necessary conditions are that you have a mind, are conscious and have mental states. This is not sufficient. As addressed above, one must be self-conscious, be able to form a conception of who they are, think for themselves momentarily and what they would be like in the future but also imagine themselves in hypothetical situations and their actions in such circumstances. However, this is not sufficient either, as animals are capable of these things, they are conscious beings also.
For example, an animal could be hungry (thinking for themselves at a present moment), and know if they eat they would satisfy that hunger (they know what they will be like in the future). They know hypothetically is they were to catch their prey, they would know what to do in that situation. Yet, a person can ascribe thoughts, emotions etc. They can describe what they are doing or intending to do. Overall, a person can evaluate and reflect themselves, a key difference between animals and humans. Animals merely cannot reflect on their desires, they have the inability to evaluate situations.
But most importantly, a person can communicate, unlike an animal a person can use language. The incapability to reflect on themselves (first and second order desires) is mainly due to the fact that they cannot use language. Language is the main criteria as to what differentiates the concept of a person to an animal. If we lacked the ability to speak to one another, we would have no ethical judgement. This is why we disregard any moral blame or praise when considering the actions of animals. They have no systems of law, schools, government etc. Such things require language.
On the other hand, it is possible to hold an alien morally responsible for things they may have done, providing they are identifiable as a person. Further, a person is able to command first and second order desires. First order desires being, to want something – second order desires being simply to want not to want something. For example, diets. You want to resist eating food that is unhealthy; you want to not want unhealthy food. Lastly, the difference between a person and a non-person (animals) is that people can give reason and justifications for their actions and beliefs. Animals simply cannot.