Explaining the nature of consciousness is one of the most important and perplexing areas of philosophy, but the concept is notoriously ambiguous. The abstract noun “consciousness” is not frequently used by itself in the contemporary literature, but is originally derived from the Latin con (with) and scire (to know). Perhaps the most commonly used contemporary notion of a conscious mental state is captured by Thomas Nagel’s famous “what it is like” sense (Nagel 1974). When I am in a conscious mental state, there is something it is like for me to be in that state from the subjective or first-person point of view. But how are we to understand this? For instance, how is the conscious mental state related to the body? Can consciousness be explained in terms of brain activity? What makes a mental state be a conscious mental state? The problem of consciousness is arguably the most central issue in current philosophy of mind and is also importantly related to major traditional topics in metaphysics, such as the possibility of immortality and the belief in free will. This article focuses on Western theories and conceptions of consciousness, especially as found in contemporary analytic philosophy of mind.
To say you are in a state that is (phenomenally) conscious is to say—on a certain understanding of these terms—that you have an experience, or a state there is something it’s like for you to be in. Feeling pain or dizziness, appearances of color or shape, and episodic thought are some widely accepted examples. Intentionality, on the other hand, has to do with the directedness, aboutness, or reference of mental states—the fact that, for example, you think of or about something. Intentionality includes, and is sometimes seen as equivalent to, what is called “mental representation”.
The hard problem of consciousness is the problem of explaining why any physical state is conscious rather than nonconscious. It is the problem of explaining why there is “something it is like” for a subject in conscious experience, why conscious mental states “light up” and directly appear to the subject. The usual methods of science involve explanation of functional, dynamical, and structural properties—explanation of what a thing does, how it changes over time, and how it is put together. But even after we have explained the functional, dynamical, and structural properties of the conscious mind, we can still meaningfully ask the question, Why is it conscious? This suggests that an explanation of consciousness will have to go beyond the usual methods of science. Consciousness therefore presents a hard problem for science, or perhaps it marks the limits of what science can explain. Explaining why consciousness occurs at all can be contrasted with so-called “easy problems” of consciousness: the problems of explaining the function, dynamics, and structure of consciousness. These features can be explained using the usual methods of science. But that leaves the question of why there is something it is like for the subject when these functions, dynamics, and structures are present. This is the hard problem.
It is widely accepted that consciousness or, more generally, mental activity is in some way correlated to the behavior of the material brain. Since quantum theory is the most fundamental theory of matter that is currently available, it is a legitimate question to ask whether quantum theory can help us to understand consciousness. Several programmatic approaches answering this question affirmatively, proposed in recent decades, will be surveyed. It will be pointed out that they make different epistemological assumptions, refer to different neurophysiological levels of description, and use quantum theory in different ways. For each of the approaches discussed, problematic and promising features will be equally highlighted.
In a more popular view, Leibniz's place in the history of the philosophy of mind is best secured by his pre-established harmony, that is, roughly, by the thesis that there is no mind-body interaction strictly speaking, but only a non-causal relationship of harmony, parallelism, or correspondence between mind and body. Certainly, the pre-established harmony is important for a proper understanding of Leibniz's philosophy of mind, but there is much more to be considered as well, and even in connection with the pre-established harmony, the more popular view needs to be refined, particularly insofar as it suggests that Leibniz accepts a roughly Cartesian, albeit non-interactionist dualism, which he does not. In fact, Leibniz is justly famous for his critiques, not only of materialism, but also of such a dualism. (Whether Leibniz accepts, throughout his maturity, the idealistic view that all substances are simple unextended substances or monads is an important interpretive issue that has been discussed widely in recent years. We shall not try to resolve the issue here. (See Garber 2009 for comprehensive treatment.) In short, Leibniz made important contributions to a number of classical topics of the philosophy of mind, including materialism, dualism, idealism and mind-body interaction.
Philosophical work on self-consciousness has mostly focused on the identification and articulation of specific epistemic and semantic peculiarities of self-consciousness, peculiarities which distinguish it from consciousness of things other than oneself. After drawing certain fundamental distinctions, and considering the conditions for the very possibility of self-consciousness, this article discusses the nature of those epistemic and semantic peculiarities.