Note: This article was copied from Greg Koukl's site "Stand to Reason." It deals with the question of personhood and abortion.
When Is a Human Being Human?
A baby is fully human from conception. There's no question about it. Even to say that it's fully human is missing something. Jot this down. The law of identity: a thing is itself and not something else. What that means is that whatever a thing is it remains what it is for as long as it exists. Things don't change from one essential thing into another essential thing.
A simple response to give, next time someone tells you an unborn baby is a "human being but not a person."
People say, what if you became a cat? It's impossible for you to become a cat because a cat is a different essential substance. If you became a cat, one could ask the question, what is it about the cat that is the same as what you were? There is nothing about a cat that is remotely human, and there is nothing about a human that is remotely cat. Even the soul of a cat is a different kind of soul than a human soul so you could never become a cat. You would be destroyed and some cat created in your place or maybe molded from your physical molecules, but that wouldn't make you the cat.
Things don't change their essential nature. What they change is their properties. They get bigger, smaller, different color hair, they change their textures, they grow appendages. But what they are doesn't change. You were five or six pounds at one point in your life, now you're much larger. Just because you're bigger doesn't mean you're more of a human. There's more of your physical body, but you are not more of yourself. You are still the same self that you were -- human. You are fully human when you're conceived; you're fully human when you're born; you're fully human when you're twenty times the size you were when you were born. Your properties changed; your essential character didn't. The nature of your humanness doesn't change.
Now, when a being is brought into being, that being stays itself forever until it's destroyed. It doesn't become more human because humanness is not a quantitative kind of thing. If that were the case we'd have to say that people who don't have certain characteristics or have less of those characteristics than others are less human. If humanness was self-consciousness, for example, then those who are more highly in tune with themselves are more human, and those who are less in touch with themselves are less human. If it was intelligence, then those who are more intelligent are more human and worthy of more rights, and those who are less intelligent are less human and not worthy of the same kind of respect.
What we're talking about are the changes in attributes or, technically speaking, properties. We're not talking about changes of the nature. So when the new human being comes into existence at conception (by the way that is an unarguable scientific reality, it is not open to debate anymore) that being remains itself until it's extinguished from existence. The being that comes into existence from the joining of two human beings is also a human being. It's the Law of Biogenesis that everything recreates according to its own kind. It is not possible for two human beings to produce an offspring that is not of the same kind, that is non-human. The humanness is a fact from the point of conception. It is fully human. There is no gradation in that regard. There are merely gradations of development.
That point is conceded by the more sophisticated philosophers arguing for choice on the abortion issue. You will find a lot of people who aren't sophisticated who use this and quite a lot of other bad arguments. What they have tried to do is make a distinction between humanness and personhood but you run into the same problem.
How do I know that the unborn is a person from conception? Because it's a human from conception. Human beings are personal type beings. Personhood is a quality that inheres the very nature of a human. It is not a property that is developed later on. A human is a personal kind of being. There are other personal beings, by the way. Angels, for example. Or God, theoretically, if He creates and has personal attributes. The attributes don't make Him personal, they just allow us to identify Him as the personal being that He is. So there may be other beings that are personal, but there are no human beings that aren't personal because all human beings are personal beings. So personhood is the larger category, humanness is the smaller category. I know personhood starts at conception because it is a characteristic that inheres the nature.
Now, someone might not be willing to accept all that philosophy and you may not be able to articulate it well. That's okay. Here's a simple way out. When somebody says it's a human being but not a person, you ask them what's the difference? It's a fair question because they're apparently offering you a rationale why it's okay to take the life of another innocent human being who can't defend itself but is in the way. So you say, if you're argument based on personhood is so weighty that it can justify taking the life of an innocent human being, then it seems reasonable that you have a very clear fix on what a person is if it's not the same as being human.
Now, 99 times out of a hundred you won't get an answer because they've never thought it though. This is a rhetorical throwaway. It's a way of ending the discussion. It's a way of putting their point of view in your face and shutting you up. So you just toss it right back to them. What's the difference? Sometimes you will get someone who tries to set up some criteria for personhood. There are two additional responses to a list of attributes for personhood. Ask, where did you get the list? If the list is merely arbitrary then why don't you make up a list too? A person is someone who has white skin. If they argue with you, then you can ask them how they justify their list but disallow your list.
The second problem with all of those lists is they always disqualify people who are clearly and undeniably human persons. They say self-awareness is a criteria. Then what about people who are in comas? Are they not persons? Some extreme people will say that, by the way. If they aren't persons then they have no rights and we can justify doing all sorts of things to them. Some will say self-awareness is a criteria. A child a couple months old can't distinguish between himself and his surroundings so they would not be persons. Some people like James Rachels will say that they aren't a person and we can kill infants. You'll also have a problem with the personhood list in that you'll have humans who are clearly persons who are disqualified by the list, but you'll have other beings which qualify, like chimpanzees and gorillas. Those are the problems with the lists.