Subjectivism describes the fact that we cannot know everything, or even know anything for sure. Because everyone's mind is wired different everyone experiences events differently. This is epistemology 101, as debated by the most ancient philosophers thousands of years ago1.
We see colors via "rods" and "cones" in our eyes. The rods, color-vision, come in three types receptive to red, green and blue. Our responses to colours and patterns of colours is altered by our early upbringing; people who are subject to extreme conditions (such as solitary confinement) can end up with depth sensitivity and colour perception that is radically different to other people. Also, genetic differences mean that some people can have radically different perception of colors.
A person born in the countryside develops naturally a more subtle and richer perception of countryside colours, but a person born in the city will distinguish between grays more readily, and to him countryside colors all look a bit more similar than they do to a person accustomed to them. Our life experiences and upbringing affects the clarity with which we see colours. As no two people have the same experiences, all people do view colours slightly differently for both genetic and historical reasons.
Although objective reality remains the same, the limitations of our basic senses means that all individuals literally see the world differently. Subjectivism would be a boring topic if this was the extent of our epistemological problems, however. We could simply (as we have done) construct machines and devices that can see more clearly and accurately than we can, measuring colours precisely according to wavelength. Subjectivism, however, extends not only to all our senses, but to all of our thinking, as our very thought patterns are changed from our interaction with our environment: an interaction that is dominantly driven by our imperfect senses.
The neurones and chemistry that make up our brains is fundamental to our experience of the outside world. Our neurology is formed by our biology and genes, the rest by our experiences and environment. In all areas of development, which result in us thinking in the way we do, change and variation occurs that occurs in no-one else. Everyone is unique; the neural networks that make up your brain and form your thoughts are different to those that form other peoples' thoughts.
“Despite the fact that the structures of the brain which give rise to conceptual abilities and self-consciousness arise at the level of species, there is no uniformity between individuals. [...] In consequence it can be asserted with confidence that no two individuals will experience the external world in exactly the same way. Edelman (1992) draws this point out clearly when he claims that the collection of individual and subjective experiences, feelings and sensations associated with awareness are unique to each individual. These experiences, feelings and sensations are termed qualia and they will be subtly different between individuals because the same synaptic pathways which underpin neural structures are never repeated.”
All of our knowledge about everything is incomplete. Every being only ever sees a tiny fraction of reality, and all our logic, emotions and heuristics are instinctive best-guesses. Any theory about reality, from routine physics theories to outlandish religions, rely on the shared experiences of mankind. Yet even if you combine the efforts of millions of people you do not guarantee that in consensus, you find actual truth. The entire Human species has been wrong about major parts of reality - the Earth is not flat, for example. If mass belief isn't a guide to what is true, then, how can any individual ever ascertain truth, amidst his own personal limits of knowledge?
Robin Le Poidevin is Professor of Metaphysics at the University of Leeds. He highlights this problem on his book on time and space quoted from below. What he mentions with reference to time equally applies to measurements of distance, and eventually, to the description of all events and realities.
“Although we could perform a test that would show some kinds of timepiece to be more accurate than others, it [is] impossible to tell whether an instrument was 100 per cent accurate since all one had to judge accuracy by was other instruments, whose accuracy could always be called into question.”
"Travels in Four Dimensions: The Enigmas of Space and Time" by Robin Le Poidevin (2003)3
“We all suffer from systematic cognitive dysfunctions; they infuse the very way we notice and analyse data, and distort our forming of conclusions. Emotional and societal factors influence our thinking much more than we like to admit. Our expectations and recent experiences change the way we recall memories. Even our very perceptions are effected by pre-conscious cognitive factors; what we see, feel, taste and hear are all subject to interpretation before we are even aware of them. Our brains were never meant to be the cool, rational, mathematical-logical computers that we like to sometimes pretend them to be.”
Everyone sees things differently because everyone has different information, and everyone's brains are wired different. The same fact presented to two people will be interpreted and stored in two different ways. It's almost as if there is no "real" world... just millions of versions of the world and we just haven't got the mental power as living beings to see what is real and what is not outside of our own experience. Consensus is a diplomatic compromise this gives us shared experiences, cultural assumptions and explanation, and theory about the world. To rely, however, on logic and reason leads to problems where one person concludes that another's experience is false. For example a psychiatrist concludes that a patients' experience of government conspiracy is a false experience - even though it's an experience the person has been having consistently for ten years - at the end of the day it's only one persons' point of view versus another and logic is not self-affirming of the world, only self-contained. These epistemological problems undermine any effective employment of any idea of objective reality.
Even if absolute morals could be perceived or were inherent within us, then because all of our brains are different, every person interprets that moral differently, according to their particular neural history, and no two people would comprehend exactly the same concept. It is impossible to communicate the absolute. It is impossible to dictate an absolute moral using natural methods. Within the scope of Human experience, objective morals do not exist. This has particular implications for religion and some religion's claims for absolute morality. It seems that the creator has specifically gone out of its way to avoid the imparting absolute morals.
For more on topics like this, view: Religion and Morals
This leaves us with the theological implications of the impossibility of the perception of objective reality:
God specifically doesn't want us to know the absolute.
God specifically doesn't want us to know absolute morals. Perhaps this is why religions, as reported by the likes of Moses, has been temporal and local, rather than transmitted directly into all people's minds by God (which would be the technique it would use, if it wanted us to know something absolute). (See: "God's Methods of Communication: Universal Truth Versus Hebrew and Arabic" by Vexen Crabtree (2012))
There are no knowable moral absolutes.
Morals are created by God to suit particular cultures and people, hence, why there are so many revealed religions and why things that are seen as good in one society are seen as bad in another. Therefore even religious morals are temporary and ad hoc both between different religions and between different branches of the same religion.
And finally, much more likely given the evidence:
Morality is purely cultural and subjective and does not come from God at all.
It is possible that everything that you see, the entirety of what you consider "reality" is complete illusion. You could be completely insane, and suffering from grand delusions, where nothing that you see corresponds to reality. You could be in a straight jacket, hallucinating your life away. This is possible - part of reality disorders (e.g., paranoia) is that you do not know what is real or not4. Consider an even more extreme position (thankfully one which I think is untrue):
“Solipsism is at the most extreme end of subjectivism. All people see things differently, so differently that some say everyone experiences a different reality and there is no real way to verify if there an objective reality at all, aside from what is observed. Go as far as subjectivism takes you, and you arrive at solipsism.
Solipsism is the belief that your own mental states are the only states: Only your self exists, nothing else. All is a creation of your imagination, including other beings. Other beings, who may appear to be alive, are actually just projections of your own being.”
Quantum Physics is a vastly important area of physics for philosophers, most philosophers have (or should have!) a running interest in quantum physics, and I would guess that all the greatest scientists in this field have strayed long and hard into epistemology and the metaphysics of philosophy.
Heisenburg's Uncertainty Principle is the fact in quantum physics (the study of miniscule particles) that if you observer/measure a particles precise position, you cannot know its speed, and vica versa. This phenomenon is a mathematical catch 22 - it is impossible to measure one thing without altering another. Also all observation slightly changes what is being observed. So even with the most expensive and accurate scientific equipment, measurement causes error and a lack of knowledge. At a very fundamental way, at the height of science, we know that we cannot obtain absolute knowledge.
We all experience things differently. The same event is experienced in a different way by everyone and everything that witnesses it. This is because everyone's brain is wired up slightly differently, on account of their genotype and phenotype, upbringing and expectations. Given that this is all incontrovertible, how is it then we can share our experiences, and live in a common world, rather than individual solipsistic universes?
The answer is that we arrive at a reality by consensus. We all call the sun "yellow", no matter what actual shade we see the sun as - and despite the fact that we only see a fraction of wavelengths that the sun emits because our eyes themselves can only see certain wavelengths. We all put "happiness" and "sadness" on the same scale, even though we all experience them to different extents, and we all describe the world in standard ways using our languages, basing our communications on shared understandings of what the words mean. This is because although we experience things different, we can still try to communicate ideas to each other.
We point at things and give them names. Each person who looks at a thing will see it from different perspectives, have that thing invoke different memories and emotions, and think about that thing with different neurones and thought patterns. We might as well say that one person sees Object A and another sees Object B and there is simply no way for them to agree. But us Humans are pragmatic creatures who simply like to get on with life without letting philosophical problems get in our way. So, when two people perceive this object differently, they will in general both call it by the same name, and discuss it using shared words despite differences in perception. This way, dialogues can continue. Pragmatically, the dialogue is meaningful. Subjectively, it is only semi-meaningful. For those philosophers who are passionate about objective reality, the dialogue is pretty meaningless until both people agree on what exactly they are talking about, which can never happen.
Thankfully, although everyone lives in their own perceptual and conceptual worlds, we simply call things by their names, discuss concepts by their labels, and blunder blindly on hoping that practical outcomes are more important than the epistemological problems of subjectivism. In the material world, this is perfectly adequate. It is less satisfactory when we consider ethics and religion.
Our brain is an imperfect organic machine, not a mystical repository of truth. Our senses are imperfect, our point of view limited, and the reality we experience is never the total picture. Human thought is infused with systematic thinking errors. We can logically deduce that any given experience may be untrue, and any particular thought could be a mistake. The result is that our total take on reality is a mix of guesses and patchwork. No two people ever experience the same event or thing in the same way, because the complexities and depths of their errors and assumptions are different for every person: every event is experienced slightly differently. No-one has precisely the same point of view on any event.
Everyone experiences a different reality and there is no way to reconcile the experiences of two different people. Our internal worlds are unverified. No knowledge is absolute. To accept this doubt behind every theory and fact is the scientific way - evidence and logic must back up theories, but theories are never irrefutably proven, they always remain not-yet-disproven. The psychologist William James wrote that many interpretations of reality are arrived at because people find them nicer or better for themselves:
“The obvious outcome of our total experience is that the world can be handled according to many systems of ideas, and is so handled by different men, and will each time give some characteristic kind of profit, for which he cares, to the handler, while at the same time some other kind of profit has to be omitted or postponed.”
The result of all this fog is subjectivism, the realisation that our realities as we experience them are completely tied up with personal experience and personal mental traits. Any attempts to learn "absolute" truths will fail, simply because our Human brains are not equipped to deal with reality in an objective way.
(2008) "The False and Conflicting Experiences of Mankind: How Other Peoples' Experience Contradict Our Own Beliefs" (2008). Accessed 2015 Apr 08.
(2010) "Pascal's Wager is Safer in Reverse: Picking a Religion is Dangerous Business" (2010). Accessed 2015 Apr 08.
(2014) "Science and The Scientific Method: Its Character and History" (2014). Accessed 2015 Apr 08.
Davison & Neale
(1997) Abnormal Psychology. Hardback 7th edition. Published by John Wiley & Sons, Inc. Amazon link points to a newer edition than the one I've used here.
(1997) Chaos and Intoxication. Hardback 1st edition. Published by Routledge. Alan Dean is lecturer in the School of Social and Political Sciences at the University of Hull.
(1902) The Varieties of Religious Experience. From the Gifford Lectures delivered at Edinburgh 1901-1902, first Edition printed 1960. Quotes from fifth edition, 1971, Collins. [Book Review]
Le Poidevin, Robin
(2003) Travels in Four Dimensions: The Enigmas of Space and Time. Published by Oxford University Press, Oxford, UK. The author is Professor of Metaphysics at the University of Leeds.
Russell, Bertrand. (1872-1970)
(1946) History of Western Philosophy. Quotes from 2000 edition published by Routledge, London, UK.