A 50th anniversary edition of one of the most widely influential articles of 20th Century philosophy "Consciousness is what makes the mind-body problem really intractable." So begins Thomas Nagel's classic 1974 essay "What is it Like to be a Bat?" Nagel's essay initiated the now widespread attention to consciousness as a central problem for philosophy, psychology, and neuroscience; it also influenced the recognition of the consciousness of nonhuman creatures as an important subject of study.
Nagel argued that the essential subjectivity of conscious experience -- what it is like for the creature undergoing it -- means that reductionist theories of mind, which attempt to analyze it in physical terms, can never succeed. It follows that the physical sciences cannot provide a complete description of reality, and that the physical conception of objective reality must be transcended if science is going to comprehend the mind.