His criteria for personhood are that the animal must be able to desire things, to act in an intentional manner to acquire those things, and must have a sense of self i.e. the animals must know that s/he exists.
Hans kriterier er at dyret skal være i stand til at ønske ting, skal kunne handle forsætligt efter at få fat i de ting og skal have en selvbevidsthed – altså vide at det eksisterer.