Some of both his fiction and non-fiction books and papers have dealt with intelligence and consciousness. Larry Hauser credits Leiber's dialogue, "Can Animals and Machines Be Persons?" for articulating the claim that "the solipsistic predicament pertains to individuals not species," so that if one can reliably tell that other humans have minds it would be sheer chauvinism to maintain one could never know whether something non-human had a mind. Lesley McLean comments that "Justin Leiber, who Dennett cites as a source for exposing certain hidden agendas distorting objective research into animal consciousness, himself offers a subjective account for why indeed we might doubt the link between moral standing and having of a mind 1988...What is interesting is that neither Descartes nor Leiber thinks animals to be conscious, yet they nevertheless think them worthy of moral consideration." Peter Singer, Mary Midgley, and others cite L. C. Rosenfield's "From Beast-Machine to Man-Machine: Animal Soul in French Letters from Descartes to LaMettrie" (New York, Oxford University Press, 1941) for a ghastly account of animal cruelty by unnamed Cartesians, but Singer and the rest fail to mention that Rosenfield dismisses the account as a pious anti-Cartesian fabrication, and further, that Rosenfield maintains that Descartes himself was never accused of cruelty to animals, nor did Descartes maintain that animals could not feel pain(Leiber 1988).