DrSinger: Summary
Summary of Issues: Steel-Manning and Interpreting NTT
It will be most helpful to put the basic reasoning of the first part of NTT in its simplest form. Without any commitment to what it is for us to think that an entity has moral value (for discussion of this see Defense of the First Part's Premises), the argument invites us to reason essentially as follows:
- (P1) All sentient humans have moral value
- (P2) There is no trait absent in sentient non-human animals which is such that, if the trait were absent in a counterpart to a sentient human, then they would be not have moral value.
- Therefore, (C) All sentient non-human animals have moral value
Here we have introduced the notion of the counterpart to a sentient human, to mean a replica of a human with the trait removed, that does not have to remain a sentient human.
As we will see below, the reason this fails is that it is possible to claim that there exists a sentient nonhuman animal that lacks moral value, and that for all traits, human counterparts retain moral value with the trait removed.
Ask Yourself has argued that if one were to lose all of the traits that distinguish one from a non-human animal, then the resulting entity would be identical to that non-human animal, so P1 and P2 so interpreted entail C. The problem with this claim is that it presupposes something like the identity of indiscernibles: that if two entities have all of the same properties, then they must be the self-same object.
This is a substantive metaphysical thesis, to which certain philosophers have objected (for discussion see [1]). But as we will see below, the much greater problem with the argument so interpreted is that it has essentially no rational force. P2 so interpreted is essentially just asserting that all sentient beings, human and non-human, have moral value. The argument thus offers little if any reason to change the mind of someone who does not already find this view plausible, and the defense of its premises offers no guidance on how to persuade such an individual.
We will first formalize the first part of NTT in first order logic. We will then show that it is invalid by providing a counterexample in which the premises are true and the conclusion false. In essence, this is a model where all sentient humans (or oneself) have moral value, all of their trait-adjusted counterparts have moral value, but non-human animals lack moral value.
