Phenomenal Consciousness
It is tricky, if not impossible, to define phenomenal consciousness and it is best illustrated by example. Consider someone who is watching a sunset. They certainly have knowledge which can immediately be used to prompt speech, reasoning and action, so the person is “access conscious”, or “aware” of the sunset. However, in addition to that, there is the experience of watching a sunset which goes beyond factual knowledge[6]. To use Nagal’s description [7], there is “something it is like” to see a sunset. There is an appreciation of beauty, there might be a sense of peace and well-being or any number of similar feelings. In other words, there is an experience over and above the physical perception and this experience is something which is difficult, if not impossible, to communicate to others. This is akin to the well known problem of how to describe to a blind person what it is like to see red. It cannot be done [8]. Or if a person has never tasted Marmite the only way to describe what it tastes like is by reference to other tastes, such as salty and yeasty. It cannot be done outside the domain of tastes. A complete chemical description of Marmite would not help in describing the experience.
The subjective and essentially private aspect of phenomenal conscious experience is developed by Soren Kierkegaard who said “human existence is a mode of being in which subjectivity is the truth and […] such truth cannot be communicated directly” [9, page 225] “Subjectivity is truth” [10].
These experiences, called “qualia” in the literature, are a characteristic of phenomenal consciousness and, although they are usually accompanied by access consciousness, they are not identical with it. It is certainly possible to have access consciousness without phenomenal consciousness as described above for the case of a computer. It is also possible to have phenomenal consciousness without access consciousness although, in humans, this is only likely to happen if there has been brain damage.
Unlike access consciousness, “phenomenal consciousness” has so far only been attributed to biological structures.
A comparison between these two types of consciousness is given in the table.
| Access consciousness | Phenomenal consciousness |
| Relates to knowledge, function, intelligent information processing, sensory perception. | Relates to experience, agency, “what is it like” |
| Is observable by third parties and can be scientifically verified. | Is only observable by the conscious subject. There is no way for a third party to know for sure that a subject has phenomenal consciousness (subjectivity). |
| In living creatures, it has a clear and usually self-evident purpose and/or can be shown to give a survival advantage. | There is no known survival advantage and, therefore, no known evolutionary driver for it to have developed. |
| It is possible , at least in known principles, to build an intelligent robot which will be conscious of its surroundings in this sense. | It is not known how phenomenal consciousness arises and therefore no way in which we can begin to design a robot which is conscious in this sense. |
| An explanation of access consciousness constitutes an “easy problem” in the sense that it is known how to proceed even if it will take much research to obtain. It is amenable to the scientific method. | An explanation of phenomenal consciousness constitutes a “hard problem” because it is not known where to start. Because the data is not publicly observable, the scientific method can be applied only, at best, indirectly. |