In answering this question I shall first consider the extent to which we know about our own mental states before considering the arguments, both mainstream and less common, that criticise the idea of exclusivity of mental states. I believe that there is insufficient evidence to argue that others are even merely equally informed as me when considering the states of my own mind. The concept of introspection is vital to the idea that we can fully understand our own mental states, through this process one can ‘treat thoughts and feelings as necessarily private objects of inner observation’.
Lycan argued that ‘introspective awareness of sensations is similar to perceptual awareness of physical objects’. Some philosophers argue therefore that this process is at the very least incorrigible, as no force exists to evaluate the accuracy of the assessment of one’s own feelings. Furthermore as there is no physical aspect to the introspective process there is no chance for scepticism to play a part, so the Cartesian dream and demon doubts are irrelevant in this instance.
However, functionalists such as Armstrong contrarily argue that introspection is merely personalised perception, which ‘may be erroneous… t is equally possible for introspection to be erroneous’. The process of introspection can also have some significant consequences for the stability of ones mental states according to some philosophers, one argument follows that simply ‘examining one’s beliefs requires self-knowledge’. Wittgenstein however argues that by introspecting you instinctively re-evaluate your beliefs and are therefore led away from observing and into thinking which only acts to alter your now constantly evolving beliefs, thus meaning you are never in complete control or completely aware of your mental states.
Shoemaker’s attack on the idea that a state of ‘self-blindness’ could exist further strengthens the idea that only the individual can know about their own mental states. His argument states that as conscious beings we understand the ‘second order’ states that serve to motivate our more primitive states, unlike for example a dog that eats without really understanding why it feels the need to eat. Shoemaker then extends this argument further to account for all other ‘orders’ of thought when he claims that ‘in denying the possibility of the self-blind man I am denying the possibility of unconscious beliefs’.
If I am therefore aware of my own mental states in their absolute entirety then it is a logical impossibility for another person to know more about them than me. There are numerous counter-arguments from different schools of philosophic thought as to why one’s mental states are not truly private. Physicalism argues that all that exists has a physical form and therefore thoughts and mental states can be traced directly to this physical form rather than being attributed to a mind separate from the body in the Cartesian dualist mould.
Developments in science such as ‘computerised mind-reading techniques’ could potentially mean that in future years all of these thoughts could be accessed from an external source, meaning a machine could possibly gain access to subconscious thoughts that you can’t retrieve. This area of subconscious thought is possibly at the greatest risk of being better known by another person as unless you accept Shoemaker’s definition there remains inaccessible thoughts, beliefs and states. The idea of self-deception is also very significant in this case as within it ‘exists a form of rationality’.
By repressing certain beliefs one is able to self deceive, for example you could convince yourself you weren’t homophobic because of the tolerant nature of today’s society and the rejection you would suffer as a result of your beliefs. Despite having convinced yourself you are not homophobic others would still be able to pick up this information from studying your subtle behavioural traits and therefore would be in a better position to judge your true mental state than you are.
However, critics would question the extent to which the individual has hidden these unacceptable beliefs within their own mind and would disagree that this process has occurred to the extent that the individual is actually unaware of them. As I have just touched upon, the obvious method of obtaining information about the mental states of others is through inference, which is forming conclusions based partly upon what one already knows of the subject.
As Alston states, knowledge of other minds can only be achieved through mediate knowledge, inferring mental states through observing behaviour therefore requires a knowledge and understanding of certain conventions associated with behaviour. A simplified example would be of a happy dog wagging its tail, but a neutral observer can only know that the dog is happy if he understands that tail wagging is the normal behaviour associated with a happy dog.
This complicates matters further as this involves Descartes’ three stages of doubt that are invariably brought up when considering perception, which drastically reduce the probability of knowing other people’s mental states as well as they do themselves. For me the only crutch that the supporters of the view in the question have to fall back on is a Berkeleyan belief in God or some other higher power with whom we are in a form of constant communication regarding our mental states and other sensory and perceptual information.
Again, one could refute this argument purely on the basis that the question refers to ‘another person’ whereas Berkeley makes it clear God was a very separate being with significantly greater powers. So, I personally believe that we do understand and can recognise our own mental states to a much greater extent than another person would be able to. Where grey areas exist in knowledge of our own mental states outsiders are very rarely if ever better positioned to examine our mental states than we are.