Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scientists. Opinions differ about what exactly needs to be studied or even considered consciousness. In some explanations, it is synonymous with the mind, and at other times, an aspect of mind. In the past, it was ones "inner life", the world of introspection, of private thought, imagination and volition. Today, it often includes any kind of cognition, experience, feeling or perception. It may be awareness, awareness of awareness, or self-awareness either continuously changing or not. The disparate range of research, notions and speculations raises  a curiosity about whether the right questions are being asked.Examples of the range of descriptions, definitions or explanations are: simple wakefulness, ones sense of selfhood or soul explored by "looking within"; being a metaphorical "stream" of contents, or being a mental state, mental event or mental process of the brain. Inter-disciplinary perspectives
Western philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. These questions remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively. Consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology, neuropsychology and neuroscience.
Patients with hemispatial neglect may also fail to recognize paralyzed parts of their bodies:  one frequently mentioned case is of a man who repeatedly tried to throw his own paralyzed right leg out of the bed he was lying in, and when asked what he was doing, complained that somebody had put a dead leg into the bed with him. An even more striking type of anosognosia is Anton–Babinski syndrome, a rarely occurring condition in which patients become blind but claim to be able to see normally, and persist in this claim in spite of all evidence to the contrary. Stream of consciousness
William James is usually credited with popularizing the idea that human consciousness flows like a stream, in his Principles of Psychology of 1890. According to James, the "stream of thought" is governed by five characteristics:
Every thought tends to be part of a personal consciousness. Within each personal consciousness thought is always changing. Within each personal consciousness thought is sensibly continuous. It always appears to deal with objects independent of itself. It is interested in some parts of these objects to the exclusion of others.A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or "mental continuum". Buddhist teachings describe that consciousness manifests moment to moment as sense impressions and mental phenomena that are continuously changing. The teachings list six triggers that can result in the generation of different mental events.