Introspection is the examination of one's own conscious thoughts and feelings. In psychology the process of introspection relies exclusively on observation of one's mental state, while in a spiritual context it may refer to the examination of one's soul. Introspection is closely related to human self-reflection and is contrasted with external observation.Introspection generally provides a privileged access to our own mental states, not mediated by other sources of knowledge, so that individual experience of the mind is unique. Introspection can determine any number of mental states including: sensory, bodily, cognitive, emotional and so forth.Introspection has been a subject of philosophical discussion for thousands of years. The philosopher Plato asked, "…why should we not calmly and patiently review our own thoughts, and thoroughly examine and see what these appearances in us really are?" While introspection is applicable to many facets of philosophical thought it is perhaps best known for its role in epistemology, in this context introspection is often compared with perception, reason, memory, and testimony as a source of knowledge.