I simply don't grant your previous arguments. "First order" fetus rationality is neither ostensibly apparent nor a physiological possibility especially in early gestation.
I wouldn't use the term "first order." But you can refuse to grant my arguments all day long. That's not the same thing as saying: "I deny this particular premise."
Demonstrate the practical presence of rationality regarding the zygote.... beyond abstract/ideological assertion.
See below.
Notice where your equating/presuming "being human" as the equivalent to "human being". You're begging the very question here.
Qualify your assertions.
If x is a human, and "human" is being used either as a substantive adjective or a noun, then x is a human being. I see no way around this. So, let us return to our definition of person. A person, let us recall, is a subsistent individual of a rational nature. What do I mean by those words?
For a person to be a subsistent individual means that it is the sort of thing which exists in its own right, and not as the qualification of another thing. "Yellow," "6 feet tall" and "fast" are not subsistent individuals. They only "exist" as qualifications of other things. There is no such thing as "the yellow." There are only yellow things (for example, yellow flowers). Likewise, a finger is not a subsistent individual, since it is not a complete "thing" in its own right. A finger only exists as a finger insofar as it is part of a larger whole. It's a part of a complete animal.
Thus, persons are substances, not accidents.
For a person to be a subsistent individual
of a rational nature means that it is the sort of substance into whose essential definition "rational" enters. Ie, if I tell you about the sort of individual who is a person, somewhere in the description of the kind of thing that it is, I will say "and it is rational (in first act; "rational," note, in this case, tells us about the kind of thing that something is, not about what it does)."
Can something be human without being a human being? Can something be human or a human being without being a person?
By "a human being" I simply mean any subsistent individual which is human in kind. I.e., it is to pick out an individual thing and say "in addition to being a subsistent individual (and not an accident), it is human."
Can something be human without being a subsistent individual? The answer seems to be "no." We only call those things "human" which are complete, subsisting individuals in their own right. "Human" is a substantial, not an accidental term. We refer to fingers, toes and other body parts as "human" only secondarily, namely, as belonging to a complete animal.
A fetus is not called "human" in this secondary sense. A fetus is a subsistent individual, and not only that, but a subsistent individual of the human kind, and, therefore, is a human being. Since, however, the human kind is "rational animal," and a person is any subsistent individual of a rational nature, it follows that the fetus (and every human being) is a person.
The only real way to deny my arguments is to tell me that parents do not produce offspring specifically (ie, the same in species ("human being," in this case)) like themselves. You have to deny the principle that horses beget horses, that sheep beget sheep, that oxen beget oxen, and that human beings beget human beings.
But is that too ridiculous? Then we must grant that the fetus, from the moment of conception, is a person.
But you'll object that the fetus displays no signs of rationality, and that the corporeal structure of the organism is unable to sustain rational activity. I'll answer that it need only be granted that the fetus is rational in first actuality, not in second actuality, and we are assured of the rationality of the fetus in first actuality because of the general principle that parents produce offspring which are the same in species as themselves...and the parents are human beings, ie., rational animals. In answer to your objection that the corporeal structure of the organism is unable to sustain rationality, I'll answer that reason/intellect is not the actuality of a body and is, in and of itself, wholly incorporeal.
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