According to the Stanford Encyclopedia of Philosophy, introspection is a process by which one acquires direct knowledge of one's own mental states or processes. It need not imply that one can know all mental states and processes, merely that some mental states or processes can be known directly by the person experiencing the mental state or process. (See http://plato.stanford.edu/entries/introspection/)

Introspection is thought to give one privileged knowledge that others can not have, often is thought to be more direct and reliable than empirical observations, and sometimes is considered infallible. In What Does It All Mean?, Nagel employs introspection when discussing knowledge of the physical world and relies on it when discussing knowledge of other minds

Some philosophers conceive thought experiments about their introspective insights. A well-known contemporary example is the philosopher David Chalmer's thought experiments about zombies:

For Chalmers, since a zombie world -- a world that is physically indistinguishable from our own but lacking conscious experiences -- is conceivable, it follows that a zombie world is a metaphysical possibility; and, since a zombie world is a metaphysical possibility, it follows that some form of dualism is true. It follows from introspection and Chalmer's zombie thought experiment.

For philosophers such as Nagel and Chalmers, introspection and thought experiments are essential philosophical tools providing knowledge that can not be obtained through researched observations; and their results reveal a dualistic alternative to science's materialist explanations.

In "The Impact of Neuroscience on Philosophy," Patricia Churchland criticizes conceptual analysis, which she notes, "starts with what introspection reveals" and then, "via reflection and maybe a thought experiment," reaches conclusions about the mind. Unfortunately, Churchland continues, "the brain is not rigged to directly know much about itself." The point is not that introspection is useless. But she doesn't consider conceptual analysis a reliable alternative to researched observation. She considers researched observations a corrective for unreliable introspective speculations about the nature of consciousness and the mind.

The implications can seem radical. For example, in the following video, Churchland suggests that introspective accounts of "memory" and "will" are mistaken and should be eliminated, replaced by accurate accounts of the brain's multiple abilities:

So who's right? Should we give priority to introspective accounts of mind, the types of arguments that Chalmers use to justify Dualism, and Nagel uses to question our knowledge of the physical world and other minds? Should we give priority to researched observations, which lead Churchland to a materialist account of mind, as well as the claim that "memory" and "will" are folk psychological myths that should be discarded?

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