Subjectivism

Ayer, A. J. Language, Truth, and Logic. New York: Oxford University Press, 1950. The most famous early account (originally published in 1936) of noncognitivism; oversimplified by today's standards, but vividly written, very accessible, and still worth the read.

Blackburn, Simon. Essays in Quasi-Realism. New York: Oxford University Press, 1993. A sophisticated account of projectivism which is a central component of Hume's moral philosophy.

Gibbard, Allan. Wise Choices, Apt Feelings. Cambridge, Mass.: Harvard University Press, 1990. By far the most sophisticated development of noncognitivism.

Harman, Gilbert. The Nature of Morality. New York: Oxford University Press, 1977. An influential argument against moral objectivity; very accessible.

Hume, David. Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. Oxford: Oxford University Press, 2000. Originally published in 1739–1740. Book III contains Hume's views on ethics, including his seminal defense of subjectivism; accessible.

Nagel, Thomas. The Last Word. New York: Oxford University Press, 1996. State-of-the-art defense of objective standards for many sorts of reasoning, including moral reasoning.

Sartre, Jean-Paul. Being and Nothingness: An Essay of Phenomenological Ontology. Translated by Hazel E. Barnes. New York: Philosophical Library, 1956. Sartre's magnum opus, originally published in French in 1943. Difficult.

Williams, Bernard. Ethics and the Limits of Philosophy. Cambridge, Mass.: Harvard University Press, 1985. A sustained and subtle argument against various forms of objectivism—particularly those inspired by Aristotle and Kant—in ethics. Difficult in spots, but repays the effort.