Unborn children are far from sentient and your liberal use of its definition doesn't change that.
I understand. I get it. You would rather play at being the philosopher than take on the actual facts as they apply to abortion. When the facts are considered, you lose every time. That being the case, why do you believe that you would have any more success by attempting to philosophise a rational justification for killing a human being out of convenience. Even philosophers must operate in the realm of truth if they are to be effective.
At the root of it, personhood is the issue isn't it? No one on the pro choice side of the argument can make a rational argument that unborns aren't living human beings so eventually, you drag out personhood (or some equivilent) (sentience) in an attempt to make a pseudo credible argument justifying killing another human being for reasons that seldom amount to more than convenience.
It is possible via philosophical reasoning rationally answer the question of what is a person because we are persons and everyone around us are persons. It is possible to critically examinethe persons we see every day and determine whether a suggested definition of person adequately describes us.
If you look critically at some of the definitions of person that are advanced by the pro choice side of the argument, it is obviousthat most can be set aside right away without any real discussion because they simply do not mesh with our own experience of what being a person is or they are simply not applicable to the question of what it is to be a person.
First, we don't "get to be" persons because we become autonomous, or independent, or even viable. These characteristics can be dismissed out of hand as not being essential characteristics of personhood because we all know someone or of someone who lacks some or all of these characteristics to some degree or another. In fact, we all lack them to some degree or another.
You may have to be viable to stay alive, for example but viability doesn't tell us anything at all about what it is that is staying alive and if you are going to argue philosopically, it is imperative that any prerequisite you care to demand must speak to the subject of the discussion.
Nearly all of the most popular definitions of personhood suggested by the pro choice side of the argument break down in principle, it must be clear to any critical thinker that it follows that they will also break down in practice. Failure to admit this disqualifies one as a critical thinker and identifies one as a hand wringing emotionalist. If we try to draw a line and say "beyond this point we are persons" we find rather quickly that there is no bright line in which we can say after this line we have characteristics X, Y, and Z but before this line we didn't. Unless of course, you want to limit yourself to some very arbitrary and superfical physical characteristics at which time, you enter the realm of the biological sciences and you want to argue philosophy to avoid the superior scientific argument do you not?
In attempting to set a time in which we "aquire" personhood, the pro choice side immediately enters the realm of logical fallacy.
You must "beg the question". You must first assume that this aquisition of personhood happens at a time far enough along in the pregnancy so that abortion becomes a rational action and then try to construct an argument that proves whichever time you have arbitrarily set. This is a terribly flawed form of reasoning in either the scientific or philosophical arenas. The failure of the application of this rational tells us that we must first try and find the definition of personhood and then determine whether it is a thing that we aquire or not.
You suggest brain and or thinking. OK, lets go there. The potenital for reason and rational thought is a matter of kind. We either have it or we don't. Realization of reason and rational thought is always a matter of degree and we all realize it to different degrees and none of us reach the absolute limit of our potential. Agreed?
Working within that framework then, the work of being a "person" is not an issue of degree but of kind. Do you understand the difference between degree and kind? The sort of person you are is a matter of degree while what you are is a matter of kind. It is quite possible for you to be a better or worse person than someone else. You can be more or less ethical, or honest, but you simply can not be more of a person than someone else. To suggest so is nonsense.
The demand for some sort of actualization that the pro choice side argues for is based on the acknowledgement that the potenital for reason and rational thought is already there in each individual regardless of age. The pro choice side attempts to treat this as irrelavent, but if one is attempting to make a rational argument, then it simply must be acknowledged that we are all the same kind of entity as the unborn and that the adult is no more and no less than a grown up unborn. The pro choice side may argue that they are only asking that we all agree on some "reasonable" minimum qualification for personhood, but once again, in principle this demand breaks down.
The first sign of breakdown in principle is obvious on its face. The problem of having to name the degree of potential that must be achieved in order to be a person. Look about you among the various pro choicers. There simply is no agreement even among those on your side. The passion with which you hold your conviction is not a substitute for a rational explanation of why you may choose one point and another pro choicer may choose another. It also fails as reasonable substitute for a rational argument that higher and higher standards for personhood be met, even among post natals.
Then there are those who attempt to avoid the inevetable arguments by engaging the question of realizing potential as a sort of ticket to personhood. That is to say that they argue that we must reach a certain level in order to be considered a person, but once we are there, injury or illness that might bring us below that level will not "un-person" us. In this manner, they attempt to restrict the debate to those who are yet to be born. Again, to a critical thinker,
this line of reasoning fails in that it attempts to change degree into kind but doesn't allow kind to be changed back to degree.
This line of thinking ignores what is required to be a person and focuses instead on what is required to "get to be" a person. This is a dead end because even if you conceed that more is required to get to be a person than is required to remain a person then we are necessarily brought back to what is to be required to remain a person after one has achieved personhood. Such arguments would fail to oppose infantacide in a great many cases and would fail to oppose killing of older individuals in just as many cases.
The logic in introducing degree into the definition of person rather than kind is simply flawed.
Our rights are founded on the kind of being that we are, not the degree to which we achieve our potential. The extent to which we are different from each other in degree is not the source of our rights. It is nothing more than evidence of differences in our ability to exercise our rights and we all know that there is no requirement to exercise a right in order to have it none the less.
If the philosophical concept of what is a person refers to anything at all, it refers to something that doesn't need to be proven over and over. The essence of the person is something that is inbred. It is not something that we aquire somewhere along the line.
Things that are aquired can be lost and may or may not be regained again. The fact that you are a person and can not lose that personhood no matter what may befall you is evidence that it is not an aquisition that you can lose. It is simply what you are.
It simply isn't rational to argue that non persons change into persons. To make such an argument is to argue that we undergo a radical and essential change in our natures during the span of our lives.
The problem with that thinking is that if the change is inevetable from the time we are concieved if given time then the change is not a change in our essential nature. If we initiate the change from within ourselves then it must be in our nature from the beginning and any changes in characteristics like independence, or where we live, or the amount of physical development we have achieved or how much mental capacity we have later in our lives is
nothing more than a manifestation of what we were at the beginning of our life.