To translate the argument into symbolic form, we can use the following translation key:
M: Animals are mere mechanisms.
P: Animals feel pain.
S: Animals have souls.
R: Animals have a right not to be subjected to needless pain.
D: Humans have a duty not to inflict needless pain on animals.
The argument can be translated as follows:
1. (M ∨ P) (Either animals are mere mechanisms or they feel pain.)
2. ((P ∨ S) → R) (If either animals feel pain or they have souls, then they have a right not to be subjected to needless pain.)
3. ¬M (It is not the case that animals are mere mechanisms.)
Now, let's use the first eight rules of inference to derive the conclusion of the argument:
4. P ∨ S (Disjunction Elimination, using 1 and 3)
5. R (Modus Ponens, using 4 and 2)
6. ¬R → ¬P (Contrapositive of 2)
7. ¬R (Modus Tollens, using 6 and 3)
8. ¬P (Disjunctive Syllogism, using 4 and 7)
Therefore, we can conclude that animals have a right not to be subjected to needless pain (¬P).