Traditionally this has been regarded as the domain of thought and inference, marking the contrast with perceptual experiences and other mental phenomena such as pains and itches. Sensations, perceptions, and feelings are all distinguished from episodes of cognition since they provide input to the domain of thinking and reasoning but are not thoughts themselves.
More recently, cognition has been conceived as the domain of representational states and processes studied in cognitive psychology and cognitive science. These are phenomena involved in thinking about the world, using a language, guiding and controlling behaviour.
The Oxford Companion to Philosophy, ed. Ted Honderich, Oxford University Press, 1995

cognitive. Denoting mental processes connected with understanding, formulation of beliefs, and acquisition of knowledge, and thus distinct from volitional processes, such as wanting or intending.
Antony Flew: A Dictionary of Philosophy, Rev. second ed., St. Martin's Press, 1979

Etymology: Latin cognitio, from cognit-, pp. stem of cognoscere = get to know, perceive, investigate, from co- + gnoscere, inchoative of gno- (see also know), from Greek γιγνώσκω . Scholastics knew of various kinds of 'cognitions': cognitio intuitiva, c. abstractiva, c. distincta, c. speculativa, c. practica , etc.

...that underneath is an absolute unconscious which has nothing to do with our personal experience. This absolute unconscious would then be a psychic activity which goes on independently of the conscious mind and is not dependent even on the upper layser of the unconscious... It would be a kind of supra-individual psychic activity, a collective unconscious, as I have called it, as distinct from a superficial, relative, or personal unconscious. (p. 35)
The collective unconscious contains the whole spiritual heritage of mankind's evolution, born anew in the brain structure of every individual. His conscious mind is an ephemeral phenomenon that accomplishes all provisional adaptations and orientations... The unconscious, on the other hand, is the source of the instinctual forces of the psyche and of the forms or categories that regulate them, namely the archetypes. (p. 45)
I would like to emphasize that we must distinguish three psychic levels: (1) consciousness, (2) the personal unconscious, and (3) the collective unconscious... The collective unconscious...as the ancestral heritage of possibilities of representation, is not individual but common to all men, and perhaps even to all animals, and is the true basis of the individual psyche. (p. 38)
C.G. Jung: The Structure of the Psyche, in ed. Joseph Campbell, The Portable Jung, Penguin 1976

1. In general, the kind of opinions about life at large that philosophers believe unphilosophical people take for granted. 2. (in Aristotle) The faculty that integrates the data of the five senses into unified apprehensions of objects.
Antony Flew: A Dictionary of Philosophy, Rev. second ed., St. Martin's Press, 1979

Thomas Reid, a staunch apostle of a strong role for common sense in philosophy, treated the invocation of common sense as ultimately an appeal to certain innate principles of human nature that are partly constitutive of what it is to reason.
The Oxford Companion to Philosophy, ed. Ted Honderich, Oxford University Press, 1995

The Oxford English Dictionary lists a variety of meanings for the expression. Three of these, referring to mental endowment, might be taken together: ordinary understanding - without which a man is out of his mind, or feeble-minded; ordinary, practical, good sense in everyday affairs; and the "faculty of primary truths." ... A further meaning must be noticed: "the general sense, feeling, or judgment of mankind...". Here common sense seems to be a cluster of beliefs or persuasions, somehow "felt" to be true by most people.
The Encyclopedia of Philosophy, ed. Paul Edwards, Macmillan 1967, Volume II, p. 156.

complex: from Latin complexus, complectere = surround, embrace, encompass, comprise, from com- + plexus = woven.

1. a whole made up of complicated or interrelated parts.
2. a group of obviously related units of which the degree and nature of the relationship is imperfectly known
3. Composed of two or more parts; composite; not simple; as, a complex being; a complex idea.
4. Involving many parts; complicated; intricate
5. Theory of complexity: scientific discipline that studies nonlinear, non-predictable systems.

To understand the meaning of complexity in science, especially in the new theory of deterministic chaos, see What is Chaos? .

I understand complexity in the sense modern theories of deterministic chaos and complexity define it, except that I apply the term to philosophical thinking. In Essay Nature and Development of Transrational Thinking) I identify complexity with holistic thought:

Philosophers think holistically and on a meta-level of rational thinking. That's why they are dealing with a greater complexity. Complexity means here the whole instead of only parts. Holistic thinking is complexity thinking (not complicated or confused thinking). These complex concepts can be as accurately as the simpler concepts of common-sense or science. Even in modern physics, the boundary between rational and speculative (holistic) thinking begins to get smeared. The growing complexity of concepts in quantum physics breaks the narrow confines of rational thought.

The term is the modern replacement for the older term "idea", stripped of the latter's imagist associations, and thought of as more intimately bound up with language.
The Oxford Companion to Philosophy, ed. Ted Honderich, Oxford University Press, 1995

To have a concept 'x' is.... (a) to know the meaning of the word "x"; (b) to be able to pick out or recognize a presented x, or again to be able to think of (have Content/images or ideas of) x when they are not present; (c) to know the nature of x, to have grasped or apprehended the properties (universals, essences, etc.) which characterize x's and make them what they are.
The Encyclopedia of Philosophy, ed. Paul Edwards, Macmillan 1967, Volume II, p. 177

All cognitions, that is, all presentations consciously referred to an object, are either intuitions or concepts. Intuition is a singular presentation (repraesentatio singularis), the concept is a general (repraesentatio per notas communes) or reflected presentation (repraesentatio discursiva). Cognition through concepts is called thinking (cognitio discursiva). Concept is opposed to intuition, for it is a general presentation or a presentation of what is common to several objects, a presentation, therefore, so far as it may be contained in different objects....((section)1)
The matter of concepts is the object, their form is generality.... ((section)2)
The concept is either an empirical or a pure one (vel empiricus vel intellectualis). A pure concept is one that is not abstracted from experience but springs from the understanding even as to content... The empirical concept springs from the senses through comparison of the objects of experience and receives, through the understanding, merely the form of generality. ((section)3)
Immanuel Kant: Logic, I, 1, (section)1-3

cf. Kant: Concepts without factual content are empty; data without concepts are blind. Therefore it is necessary to make our concepts sensuous, i.e., to add to them their object in intuition, as it is to make our intuitions intelligible, i.e., to bring them under concepts.
Critique of Pure Reason, B75

The noun Begriff means both 'concept' and 'conception', especially in the sense of 'ability to conceive'. Eckhart used it for the Latin conceptus or notio; and Wolff used it in the sense of a 'representation of a thing in thoughts', but its meaning was stabilized by Kant: in contrast to 'intuition (Anschauung)', the concept is a 'universal representation (Vorstellung) or a representation of that which is common to several objects'.
Michael Inwood: A Hegel Dictionary, Blackwell 1992

In Essay Knowledge and Information) I understand 'concept' in the following way:

To know something means to have a true concept of it. A concept is true if it expresses the essence of the object of which it is a concept. The concept is the mental abstract of a physical or experiential object. To have a concept of something is tantamount to having knowledge of it. ... The concept is the generalization of a particular object. Concepts are always universal, never particular.

Alfred North Whitehead about concrescence:

'Concrescence' is the name for the process in which the universe of many things acquires an individual unity in a determinate relegation of each item of the 'many' to its subordination in the constitution of the novel 'one'. The most general term 'thing' ... means nothing else than to be one of the 'many' which find their niches in each instance of concrescence. Each instance of concrescence is itself the novel individual 'thing' in question... An instance of concrescence is termed an 'actual entity' - or, equivalently, an 'actual occasion'. (p. 211)
An actual entity is concrete because it is such a particular concrescence of the universe. (p. 51)
The concrescence is an individualization of the whole universe. (p. 165)

Concrescence is the process of 'growing together', from Latin concrescere = grow together, join together, condense, congeal; concretum = put together, composed of, condensed.

I use the term in a similar way as in relation to subconcepts that constitute a holistic concept. These subconcepts are not analyzable parts of a holistic concept, but are 'grown together' to form an indivisible whole.
This process of 'conceptual concrescence' is the conscientious task of the transrational philosopher to translate the holistic concepts into concrete universals. These concepts may contain already known concepts, but now in a new frame of reference and related to a higher level. So, while the contained concepts can be understood separately, the transrational concrescent concept opens a new view by interrelating the sub-concepts in a new way and unite them in a new concept.

I call a perception clear (clara) when it is present and accessible to the attentive mind, just as we say that we see something clearly when it is present to the eye's gaze and stimulates it with a sufficient degree of strength and accessibility. Distinct (distincta) implies that, as well as being clear, the perception is so sharply separated from all other perceptions (sejuncta et praecisa) that it contains within itself only what is clear.
René Descartes: Principles of Philosophy, Part I, art. 45

At distincta notio est qualem de auro habend Docimastae, per notas scilicet et examina sufficientia ad rem ab aliis omnibus corporibus similibus discernendam.
G.W. Leibniz: Meditationes de cognitione, veritate et ideis; see also: Discours métaphysique, section 24

A holistic concept cannot be separated into analyzable concrete parts but is whole entity with an indefinite number of interlaced, interconnected and webbed sub-concepts or ideas or thoughts. Holistic concepts are hard to express in verbal form, i.e. words. They contain an intuitive understanding on a purely cognitive level. They are not necessarily abstract or vague, but more complex, because they do not exclude or omit important parts (like rational and empirical concepts do), but embrace even thoughts and ideas not yet recognized as being part of the whole.
Regarding the complexity of holistic concepts: Since understanding becomes more complex, so can the pertinent concepts. A complex concept can contain a host of subordinate concepts. The greater the extension of a concept, the greater its universality. That does not necessarily mean that the concept becomes vaguer and more shallow. It is the conscientious task of the transrational philosopher to translate the holistic concepts into concrete universals. These concepts may contain already known concepts, but now in a new frame of reference and related to a higher level.

A metaphysical concept is any concept that transcends pure empirical concepts, such as are derived from sense experience, perception, sensation etc. Metaphysical concepts are what Kant called the Ideas of Reason, synthetic apriori notions that can be formed by the power of pure thought and that are not dependent on experience as the only source of concepts (as empiricism and positivism hold).
Metaphysical concepts are essential and necessary to understand the whole, to go beyond the fragmentary view of the average man in order to grasp the higher interrelations and meanings of the world in toto. Science gradually recognizes that its analytical methodology does not yield understanding of the whole and that therefore a radical paradigm shift is necessary and is actually already going on. Metaphysics, after having been shunned from science since the beginning of this century, is becoming again part of a holistic view amongst scientists of all fields.

On the distinction between distinct and metaphysical concepts see Essay Nature and Development of Transrational Thinking:

Distinct concepts are communicable on a much broader level than speculative philosophical concepts. The reason for that is not the decreasing degree of distinctness when dealing with metaphysical concepts, but the increasing degree of complexity. Whereas commonly clear concepts are simple concepts, having direct empirical reference or are mathematically defined within the science community (universality), metaphysical concepts are not directly linked to empirical or scientific sources and are therefore not as easily available for understanding than the former simple concepts.

A transrational concept is related to what I call Transrational Thinking (Paranoesis). It is the most complex concept accessible to the human mind. Actually, it is not a concept any more in the traditional sense as defined above. Concepts are communicable in terms of linguistic entities, such as words and sentences. Transrational concepts, however, defy 'linguification' (Versprachlichung), that means, transrational entities can be thought but not verbalized. Transrational concepts need to be translated into communicable concepts, although this process strongly restrains the original pure and transrational thought and demotes it to the restrictory levels of conceptual thinking and thus language-dependent thought.

In fact, however, whether speaking of conceptualization or whether speaking of objectification, we are essentially referring to the same process, because at the precise moment that we form concepts about the universe we are (apparently) making that universe objective.
Ken Wilber: Spectrum of Consciousness, Quest Books 1993, p. 74

Generally, conceptualization is the act of forming a concept. In my view, empiric data or any kind of sense experience is conceptualized, that is objectified in our mind, so as to constitute the dual-valued world of subject and object we think to experience every day (s. also Essay The Identity of Subject and Object. Mind is the creator of the world we experience in so far as, in the Kantian sense, mind is the fundamental condition of every experience, makes experience possible in the first place. We do not experience the world in itself, but as modified by the categorial scheme of our mind. Real objects of the world become concepts of the mind which are essentially different from the things-in-themselves. The problem with conceptualization is that we usually confuse the concepts for the real entities. That's the nature of the practical mind whose primary task is to handle everyday situations and not to understand the underlying reality of the world.
To understand the process of conceptualization is the first step in overcoming our conceptual thinking. If we want to extend our thought to a more holistic and transrational way of thinking, rational concepts must be recognized as auxiliary means of the intellect and not as final and absolute truisms. The transcendence of conceptual thought is necessary to overcome the inherent limitations of our empirical or rational mind and to open ourselves to other side, the infinite mind, that is only accessible by means of transrational thinking or holistic thinking. Therefore, although the act of forming concepts is necessary for our daily life, it is not intransigent and final limit of our mind, but just a tiny speck in the infinite noetic space that remains yet to be discovered and explored.

Consciousness exists, but it resists definition. There are some criteria for saying of some organism or state that it is conscious. Consciousness involves experience or awareness. Human mental life has a phenomenal side, a subjective side that the most sophisticated information-processing system might lack. To paraphrase Thomas Nagel, there is something it is like to be in a conscious mental state, something it is like for the organism itself. Conscious mental states are heterogeneous in phenomenal kind. Sensations, moods, emotions, dreams, propositional thought, self-awareness all occur consciously - perhaps some of these states only occur consciously.
The Oxford Companion to Philosophy, ed. Ted Honderich, Oxford University Press, 1995

A term with two related philosophical uses: first, as for example, for Locke, in the sense of self-knowledge acquired by virtue of mind's capacity to reflect upon itself in introspective acts analogous with perception; and second, in a broader modern sense, opposed to anaesthesia, designating what is held to be the general property of mental states.
Antony Flew: A Dictionary of Philosophy, Rev. second ed., St. Martin's Press, 1979

In An Essay Concerning Human Understanding Locke defined consciousness as "the perception of what passes in a man's own mind" (II,i,19). Consciousness or reflection is a person's observing or noticing the "internal operations" of his mind. It is by means of consciousness that a person acquires the ideas of the various operations or mental states, such as the ideas of perceiving, thinking, doubting, reasoning, knowing, and willing and learns of his own mental states at any given time. ...
The term "consciousness" has a broad use to designate any mental state or whatever it is about a state which makes it mental. "Consciousness includes not only awareness of our own states, but these states themselves, whether we have cognisance of them or not....(Stout, Manual of Psychology, p. 8)....
The Encyclopedia of Philosophy, ed. Paul Edwards, Macmillan 1967, Volume II, p. 191-193

Conscious experience is at once the most familiar thing in the world and the most mysterious. There is nothing we know about more directly than consciousness, but it is far from clear how to reconcile it with everything else we know. Why does it exist? What does it do? How could it possibly arise from lumpy gray matter? We know consciousness far more intimately that we know the rest of the world, but we understand the rest of the world far better than we understand consciousness. (p. 3)
The term "consciousness" is ambiguous, referring to a number of phenomena. Sometimes it is used to refer to a cognitive capacity, such as the ability to introspect or to report one's mental states. Sometimes it is used synonymously with "awakeness". Sometimes it is closely tied to our ability to focus attention, or to voluntarily control our behavior. Sometimes "to be conscious of something" comes to the same thing as "to know about something". (p. 6)
A [incomplete] catalog of conscious experiences (phenomenal consciousness): visual, auditory, tactile, olfactory, and taste experiences, pain, other bodily sensations, mental imagery, conscious thought, emotions, sense of self. (p. 6-10)
Varieties of psychological consciousness: awakeness, introspection, reportability, self-consciousness, attention, voluntary control, knowledge. (p. 26-27)
David J. Chalmers: The Conscious Mind, Oxford University Press, 1996

Resources on the Web: The Journal of Consciousness Studies is dedicated to the scientific study of consciousness. See also Association for the Scientific Study of Consciousness . David Chalmers Home Page contains a host of web related links.

Sometimes I use consciousness and mind synonymously, as in Essay Self-Referenctiality of Reflective Thought about the self-consciousness and self-knowledge. In a narrower sense, I understand consciousness (in the above-given definitions) as the interface between the physical brain and the noetic Individual Mind. The brain-mind interaction constitutes and produces consciousness as a spatio-temporal structure of an organism or body-mind entity. In Essay The Evolution of Exonoesis I elaborate on this theory in relation to the evolution of the mind:

The Individual Mind interacts through the brain with the body and the environment. This produces consciousness as the necessary and concomitant fact of a living being. Together with the extended capacity of the brain, the Individual Mind's manifestation results in what is called Personality. Personality is the body-mind unity that is the living human being. In animals the Individual Mind is very limited and mostly restricted to biological functions (survival, drives, instincts, etc.). Consciousness is NOT an attribute of the Individual Mind, but of the Mind-Body-Entity. Interaction of Individual Mind with the brain structure produces consciousness. Consciousness is a product of mind-brain interaction.
I strongly refute the theory that consciousness or mind is a product of biological evolution. Consciousness is the product of mind-brain interaction and therefore depends firstly on the complexity of the brain structure that allows secondly a link-up with the Individual Mind. Current or future physical theories, such as quantum physics, will explain how the brain can produce the basic physical structure for creating the interface called consciousness. The brain is only responsible for the physical structure and not for consciousness itself that only emerges as a result of mind-brain interaction

Finite consciousness is a term synonymous to the next entry, Individual Consciousness. It connotes the unique, individuated mind-body entity, the specific character of a living human being. It is finite or limited, because this individuated structure (individual consciousness) is dependent on the whole mind-body entity and is restrained in its activity by the physical operations of the body, especially those of the brain. The interactions between consciousness and the body remain limited, because the body is a limited and relative entity. (cf. Infinite Consciousness)

see previous entry about Finite Consciousness. It is the unique structure of awareness and self-knowledge unique to every human being, and that embraces also the specific psychological disposition we call personality or charcacter. (cf. Collective Consciousness)

In Essay E017 I contrast finite and infinite consciousness (or Universal Mind):

...the positive state of mind is infinite consciousness, unlimited beingness. The negative state would be a limitation of the infinite consciousness. Being limited to a particular existence, in other words: individuality. The very process of limitation of infinite consciousness creates the individual mind.

Infinite consciousness is the state of awareness of the Universal Mind and it can be compared to another term I use in this context, Infinite Mind.

Consciousness, then, does not appear to itself chopped up in bits. Such words as 'chain' or 'train' do not describe it fitly as it presents itself in the first instance. It is nothing jointed; it flows. A 'river' or a 'stream' are the metaphors by which it is most naturally described. In talking of it hereafter, let us call it the stream of thought, of consciousness, or of subjective life.
William James: The Principles of Psychology, Dover Publications, Volume I, Chapter IX

The conscious stream, according to James, is personal, feels continuous, forward-moving, and in constant change. We tend to speak and focus on partiuclar contentful states. But the metaphor is designed to draw our attention to the deep and wide currents that surround, and render meaningful in particular ways, these thoughts. The 'halo of relations' surrounding and constituting each image or thought, James called the 'penumbra' or 'fringe of consciousness'.
The Oxford Companion to Philosophy, ed. Ted Honderich, Oxford University Press, 1995

The integration of lower states of consciousness into higher states is described by Lama Anagarika Govinda in his study of multi-dimensional consciousness and creative meditation:

The more the inwardness progresses, i.e. the more we approach the inner center, the more universal becomes experience, and when reaching the center we realize the full range of our conscious being, the totality of universal consciousness. Consciousness progresses in this fashion from limited to wider, from lower to higher dimensions, and each higher dimension includes the qualities of the lower, i.e. it incorporates them into a higher system of relations. Therefore the criterion of the consciousness or cognition of a higher dimension consists in the coordinated and simultaneous perception of several directions of movement within a wider unity, without destroying those individual features which had characterized the lower dimensions thus integrated.

I use the term to denote any forms of higher or expanded consciousness, or what Ken Wilber called the transpersonal states of consciousness. It is a form of consciousness that transcends the limitations of our everyday or empirical consciousness. Sometimes it means also the cosmic or universal consciousness (esp. in Eastern Philosophies) that is synonymous with my term Universal Mind or Hyponoesis. It is not an individualized consciousness, but formless and all-embracing, but it is the ground of existence for every individuated form of consciousness.

Thinking is an essentially human activity occurring in two basic forms. We may think in order to attain knowledge of what is, must, or may be the case; we also may think with a view to making up our mind about what we will or will not do. Following Aristotle, these two forms of thought may be called, respectively, contemplation and deliberation. ... When contemplation is successful, it terminates in a conclusion...
...the form of reasoning involved in contemplation may be called theoretical.
The Encyclopedia of Philosophy, ed. Paul Edwards, Macmillan 1967, Volume VIII, p. 100

Etymology: from con-templor, from templum = open space for observation. The verb connotes attentive observing, studying, considering, meditating upon. Originally it was the act of observing the sky for the purpose of augury, but later it came to mean the observation or reflection of mental matters, especially in philosophy.