Certainly it is wrong to be cruel to animals and the destruction of a whole species can be a great evil. The capacity for feelings of pleasure and pain and for the form of life of which animals are capable clearly impose duties of compassion and humanity in their case.

Freedom and Authority: An Introduction to Social and Political Philosophy p. " Oxford Journal for Legal Studies (Spring 1987) 7 (1): 1-25. Rawls also modified the principles of justice as follows (with the first principle having priority over the second and the first half of the second having priority over the latter half):
Each person has an equal claim to a fully adequate scheme of basic rights and liberties which scheme is compatible with the same scheme for all; and in this scheme the equal political liberties and only those liberties are to be guaranteed their fair value.

". He is one of the major thinkers in the tradition of liberal political philosophy. His magnum opus A Theory of Justice (1971) was hailed at the time of its publication as "the most important work in moral philosophy since the end of World War II" and is now regarded as "one of the primary texts in political philosophy.