I think it is safe to assume that a person whose head has been severed from his body is dead.
Fertilized ova also do not have heads or brains or rights.
Why do you call a zygote a 'fertilized ova'? Sperm and ova cease to exist as such during the process of fertilization, that is as parts of human beings, and a completely new human being is produced. They are no longer what they were, but have been changed into a single, whole, complete human being.
A person with a severed head is not analogous to a human zygote. The case of the person with the severed head is distinguished from the case of the zygote in that the person in the first case is dead, while our hypothetical zygote is alive. The two are not analogous.
Moreover, you are confusing the accidents of personhood with the essence of personhood. The essence of being is actual, it is the the functioning of that being which is potential or accidental. The personhood of the zygote is already existent because he must actually be in essence a human being in the first place to grow a human brain! So he is already a person with the potential to grow a brain, just as a newborn baby is already a person with the potential of speech. But perhaps you prefer to define a child who has not yet developed speech or who has speech defects as less of a person with less rights in the same way that you define a zygote who has not yet fully developed a brain as less than, or no person at all - with diminished or no rights at all. How about a two-year-old who has not fully developed her reproductive organs? Is she less of a person than a five year old or a seventeen-year-old? What if I said that the seventeen-year-old is a person because she has developed breasts and the five-year-old is not a person because she has not? But that is the absurd conclusion of your premise when taken to its logical conclusion. Human beings are personal beings. That's just the kind of beings they are, no matter what their stage of development.
What do you think personhood is anyway, and what is the difference between human and person?
Cordially
It is safe to assume that if it is on life support it is alive.
Now does it have rights?
"Why do you call a zygote a 'fertilized ova'?"
I'm happy to go along with that semantic change. Let me restate:
A zygote does not have a head, brain, or rights.
"The case of the person with the severed head is distinguished from the case of the zygote in that the person in the first case is dead, while our hypothetical zygote is alive. The two are not analogous."
You have dismissed the analogy without addressing it. The fact remains a live body without a head, or brain, or brain without a structurally intact cerebral cortex has no rights.
The zygote is analogous to the body on life support because it has no brain.
Let me put another question to you: Suppose you came upon the scene of a decapitation, and had the ability to save either the main body or the head. Which would you save?
"Moreover, you are confusing the accidents of personhood with the essence of personhood."
No, I simply don't truck with superstitions like 'essense of personhood'. Or, if there is an essence, it is in having a brain (with the structures for thought, to allow us to distinguish from animals,) which the zygote does not have.
"just as a newborn baby is already a person with the potential of speech."
Now suppose the newborn baby only had the brain structures necessary to sustain a pulse and respiration. Does it have rights?
If no, I would then pose the same question about a similar fetus at 8 months gestation, 7 months, 6 months, etc.
"But perhaps you prefer to define a child who has not yet developed speech or who has speech defects as less of a person with less rights in the same way that you define a zygote who has not yet fully developed a brain as less than, or no person at all - with diminished or no rights at all. How about a two-year-old who has not fully developed her reproductive organs? Is she less of a person than a five year old or a seventeen-year-old? What if I said that the seventeen-year-old is a person because she has developed breasts and the five-year-old is not a person because she has not?"
Now wherever did you get such silly ideas.
"But that is the absurd conclusion of your premise when taken to its logical conclusion. Human beings are personal beings."
Hardly.
The absurd conclusion from your premise ( that a brain is not necessary for rights ) leaves us with a headless body with rights.
Look, I'm really trying to understand you, but it seems perfectly obvious and commonsensical to me to say no brain = no rights (and no personhood.)