Despite their rather different philosophical foundations, both philosophers arrive at basically the same conclusions. Singer takes a utilitarian approach, while Regan takes a deontological "rights" and "inherent value" position. In the end they both take a position of vegetarianism and advocated banning animal experimentation and sport hunting. In an exchange of letters in the April 25, 1985 issue of The New York Review of Books, Regan writes: "Singer and I have been independently applying and developing very different ethical theories to . the treatment of non-human animals." He continues that "it is difficult to exaggerate the radical moral difference between Singer's utilitarianism and the rights view". At the end of Singer's reply to Regan, Singer mentions: "The practical value of Regan's book (All the dwell Therein) lies in its attack on our social practices of using animals as research tools and as mere lumps of palatable living flesh. On these practical issues Regan and I are in full agreement. Viewed from the perspective of a society which continues to accept these practices, the philosophical differences between us hardly matter.".
In 1975, Australian philosopher Peter Singer wrote a book called Animal Liberation. In this book Singer argued that humans should not use animals, all based on utilitarianism. Utilitarians say actions should be judged strictly by their consequences. An action is good if it will provide the greatest benefit to the largest number of individuals. Singer did not stop there, and said that when we calculate consequences, we must take into account the interests not only of human beings but also of animals. If we fail to consider these animals' interests, or if we give human beings special consideration, we are guilty of "speciesism." To Singer, animal research is morally acceptable if the benefits to humans or animals used clearly outweigh the harm to the animals used in the research.