A. I’ll play devil’s advocate for the sake of clarification and understanding.
Consciousness is the basis for the right to life (or, more precisely, the right to avoid the suffering involved in abortion), because the pain involved in abortion is bad. The experience is negative for the one who suffers. If there is no sufferer, because he is not conscious of his suffering, then there is nothing bad about it. The act is no different from kicking a stone, and such a neutral act should give way to the woman’s interests, since she will suffer if the fetus is eventually born.

I didn’t understand what the moral consideration is for sanctifying the life of someone who belongs to the human species simply by virtue of that fact. Is it because God intended his creation?

B. I didn’t understand. “Those capacities are realized in her” means that she is conscious of suffering, unlike in the case of the fetus.
As someone once said, a geometer doesn’t have to be a triangle, so there’s no difficulty with Tzemach 🙂

This is not about suffering but about the right to life. Those are two completely different things. You can kill an adult person with consciousness without his suffering for even a second. He won’t be aware of it. Is that permissible in your view?
The value of life is a value, and as such it cannot be grounded in something more basic. Even if you explain it on the basis of something else, you can then ask: what is the basis of that something else? Where will you stop the chain of explanation? At values. So human life is a value.
I wasn’t raising any difficulty about Adi Tzemach. I brought his argument as an example of an absurd argument of the Singer type, one that suffers from a failure to understand complexities (see the heap paradox). The parenthetical remark was not meant as an objection.

That would of course be forbidden according to Singer, since an adult person is also rational in the sense that he has “projects” he wants to complete in his life, and he does not want them cut short by murder.
I’m trying to understand the Rabbi’s position, so I’ll ask: what exactly are we sanctifying when a plant-like person who has no chance of ever waking from his coma is hooked up to machines? The mere preservation of the biological processes of the species Homo sapiens? What are those “lives” that are considered a value?
What didn’t Singer understand regarding the heap paradox?

Why is it relevant that he is rational? After he dies, he no longer exists and nobody suffers. And at the moment of death he didn’t suffer either. So what’s the problem? How is he different from an animal that has no consciousness?
I explained that we sanctify human life regardless of its condition. That is the meaning of the claim that this is a value. Don’t expect an explanation, because values have no explanations.
What he didn’t understand about the heap paradox is that there is such a paradox. When you show that there is a slippery slope, that does not mean there is no line somewhere in the middle. He takes human life and shows that there is nothing special about it apart from consciousness. But that is not true. A human being is not just consciousness. Consciousness is one aspect of the definition of a human being. The blurring that leads him to identify a human without consciousness with an animal is of the heap-paradox type. Exactly like Adi Tzemach, who doesn’t understand that there is a difference between my relation to myself one moment from now and my relation to another person. He too does not address intermediate states, but sees the situation in black and white: either there is a connection or there isn’t.

Another question: when we deal with the value of Torah study, the Rabbi would distinguish between actions not directly connected to the study itself (like flipping through the book) and the essence of the study, and presumably only that would count as the value. Beyond that, the Rabbi would also analyze the difference between study and what only looks like study, and would also distinguish between qualities of study. Why can’t the value of life be analyzed in the same way?
I remember reading from the Rabbi that the difference between a secular Jew and a religious Jew is the ritual commandments, meaning that even a murderer can be considered religious, but not someone who eats meat with milk.
Why can’t we create a list of traits that exist only in a human being (even if there are more capacities and qualities beyond consciousness) and define him by them, just as ritual commandments define a religious person, and whoever is not endowed with them would be considered on the level of an animal, just as someone who eats meat with milk cannot be considered a religious person?

Who said you can’t? The only question is what those traits are. Indeed, the definition of a thing is supposed to be based on the characteristics unique to it. And still, it is worth knowing that it is not always possible to offer an explicit definition of things, even when we understand them. I discussed this at length in the series of columns on poetry (107 and onward).