NameTheJustification

A central idea of arguments like that from less able humans (or "marginal cases") and NameTheTrait or NameTheTrait 2.0 is that, on reflection, there does not seem to be a good justification for thinking that all sentient humans have an important moral status while sentient non-human animals lack moral status so entirely that it is morally fine to treat them in the ways that consuming animal products treats them.

The argument discussed in this entry seeks to present this idea more clearly and directly.

NameTheJustification In English

In the following 'x has non-trivial moral status' means at least that we are morally required not to treat x in the ways that consuming animal products treats non-human animals - for instance, x is such that we are morally required not to inflict enormous suffering upon and / or kill x for relatively trivial reasons (like taste-pleasure).

Having such non-trivial moral status could be one way of understanding what it is to have "moral value" or what is minimally required by "an adequate expression of respect for our value" so long as we are sentient. More ambitious arguments could replace 'non-trivial moral status' in what follows by something stronger, such as having the right to the equal consideration of one's interests, etc. But because the argument for veganism requires only that sentient non-human animals have non-trivial moral status, for arguments to be as convincing as possible to as many interlocutors as possible they should, like those below, focus only upon the grounds for non-trivial moral status. The arguments below and their conclusions are entirely consistent with humans having greater moral status than sentient non-human animals, beyond the mere non-trivial moral status that they contend non-human animals share with humans.

The Simple Version

(P1) Sentient humans have non-trivial moral status.

(P2) If sentient humans have non-trivial moral status but sentient non-human animals lack this status, then there must be some morally relevant difference between sentient humans and sentient non-human animals that is important enough to justify this radical difference in moral status.

(P3) There is no morally relevant difference between sentient humans and sentient non-human animals that is important enough to justify this radical difference in moral status.

Therefore

(C) Sentient non-human animals have non-trivial moral status.

The All Sentient Humans Version

If one wants to make P3 more compelling at first sight, or make the strategy for defending P3 (with reference to less able or "marginal case" humans in various circumstances) more obvious, one can present a version of this argument that clarifies which sentient humans and non-human animals are in question. This version speaks explicitly about all sentient humans, and correspondingly clarifies that the non-human animals are the farmed (and wild) animals harmed by consuming animal products - and not simply the companion animals who some interlocutors will agree we have non-tivial moral status.

(P1) All sentient humans have non-trivial moral status.

(P2) If all sentient humans have non-trivial moral status but sentient farmed (and wild) animals lack this status, then there must be some morally relevant difference between all sentient humans and sentient farmed (and wild) animals that is important enough to justify this radical difference in moral status.

(P3) There is no morally relevant difference between all sentient humans and sentient farmed (and wild) animals that is important enough to justify this radical difference in moral status.

Therefore

(C) Sentient farmed (and wild) animals have non-trivial moral status.

In Propositional Logic

One nice thing about this argument is that its logical form and validity can be very simply and easily explained using only sentential or propositional logic (one does not have to get into predicate or first order logic). The logical form is:

(P1) A

(P2) (A ∧ ¬B) ⇒ C

(P3) ¬C

Therefore, (C) B

Where:

A = "Sentient humans have non-trivial moral status"

or "All sentient humans have non-trivial moral status"

B = "Sentient non-human animals have non-trivial moral status"

or "Sentient farmed (and wild) animals have non-trivial moral status"

C = "There is some morally relevant difference between sentient humans and sentient non-human animals that is important enough to justify this radical difference in moral status [viz. sentient humans having non-trivial moral status but sentient non-human animals lacking such status]"

or "There is some morally relevant difference between all sentient humans and sentient farmed (and wild) animals that is important enough to justify this radical difference in moral status"

The validity of the argument can be easily shown as follows:

1. A; premise

2. (A ∧ ¬B) ⇒ C; premise

3. ¬C; premise

4. ¬(A ∧ ¬B); 2,3, modus tollens [i.e. X ⇒ Y, ¬Y Ⱶ ¬X]

5. ¬A V B; 4, De Morgan's law [i.e. ¬(X ∧ Y) if and only if ¬X V ¬Y], double negation elimination [i.e. if ¬¬X then X]

6. B; 1, 5, disjunctive syllogism [i.e. X or Y, ¬X Ⱶ Y] (and double negation introduction [i.e. if X then ¬¬X], since in our case the inference is ¬A or B, A Ⱶ B)