Make your argument. Ask your questions.
Chapter 4 of Book Two offers logical arguments against abortion. If you do not see your question or argument addressed below, submit at the bottom of this page.
On page 48, you say that "nothing else needs to be added for the fertilized egg to begin developing as human beings do, except nourishment and time." But there are other things that need to be added on in order for the fertilized egg to reach its full purpose, such as education, relationships, etc.
Answer: This is true, but these are conditions that are necessary to turn the human being's powers on. They are not substantial changes to the nature of the human being itself. Besides, what you are saying is also true of all people who are born. All human beings continually need these conditions to be met in order to reach our full purpose. So the need for these conditions should not exclude anyone from the definition of personhood, or we would all be in trouble.
If your argument is right, then sperm, eggs, and other human cells should also be considered human persons because they also have the potential to find fulfillment through the transcendentals.
Answer: An egg, if left as an egg, will never direct its own development toward fulfillment through the five transcendentals. We don't see eggs forming little communities of common cause, or building schools to educate younger eggs, or hospitals to tend to sick eggs, or churches to hold religious ceremonies.
The same is true with sperm, skin cells, etc. Sperm do not show any evidence of being generous, patient, kind, or forgiving, or of having empathy.
The telos of an egg is to be fertilized. That is the definition of an egg – it is a reproductive cell produced by females, whose telos is to be fertilized by a sperm. It has the power to be fertilized, but it does not contain the power to engage in transcendental desires or activities. We know this to be true because you can study eggs for a million years, and eggs will never produce any evidence whatsoever of having transcendental desires or activities. Neither will sperm or any other cell.
However, if you study a fertilized egg and watch it over time, this being will eventually develop itself as a being who desires the same five transcendentals that you and I seek. Nothing else needs to be introduced to the egg after it is fertilized (other than nourishment and time) for it to begin its own development in the direction of human personhood. The fact that it has the power to begin its own development as an individual human being gives evidence that it contains human powers. Therefore, we have to conclude that the power to find fulfillment through the five transcendentals exists at the moment of fertilization.
Since you cannot see the human power for the five transcendentals (otherwise known as the "soul"), you do not really know at what point that power attaches itself to the unborn. Maybe it's later, like the third month, or the sixth month of pregnancy.
Answer: Take a look at the section in your book titled, "Abortion and the Principle of Objective Evidence" on page 49. It answers this question by giving a sneak peak into the "Principle of Non-Maleficence" from Book 3.