Philosophers say the key to understanding human life is answering the really big questions - Why are we here? Where did we come from? Where will we go? And so on and so forth. This has truly been a debate for the ages, one that has galvanized thinkers, philosophers, theologists and scientists for thousands of years, giving rise to the schools of thoughts of idealism and realism, two heavyweights in the realm of philosophy. Yet the dawn of the modern age, by which I mean, the nuclear-space-cyberspace triad, or what Toffler refers to, much more fashionably, as the post-industrial, information-driven 'third wave' of human civilization, has given these ancient philosophical doctrines a dose of pragmatism. It has also let the 'realists' walk happily to the bank, but more on that later.
Idealism: Philosophy and Proponents
All the choir of heaven and furniture of earth - in a word, all those bodies which compose the frame of the world - have not any subsistence without a mind. ~ George Berkeley
All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason. ~ Immanuel Kant
Idealism puts forth the argument that reality, as we perceive it, is a mental construct. That its experience is due to the sensory abilities of the human mind and not because reality exists in itself, as an independent entity. In the epistemological sense this means that one cannot know the existence of things beyond the realm of the intellect. Plato first attempted to define reality in his Theory of Forms, what he termed the actual substance of 'Things' which 'Formed' matter and perceptible reality. Yet, Plato teaches that matter is real and can be experienced as a rational living entity, it is not a mere projection of consciousness. Philosophical ideas that place the metaphysical realm above and beyond that of the physical one have been around since ancient times. Hindu Vedanta and Buddhist doctrine have idealist leanings in their proposition of 'Maya' - the illusory nature of this world and 'Brahman' - the human soul finding its way through life unto divinity, following the path of righteousness and moral propriety. The early Greek philosophers, termed Neoplatonists, after their affinity for deducing the teachings of Plato and forming them into mystical ideas, also have a similar philosophical stand point. One of its leading lights was Plotinus whose teachings about 'the one', the intellect and the soul shaped the progression of metaphysical theories between the 2nd and the 8th centuries A.D.

Idealism in the modern world owes its development to philosophers such as George Berkeley, who was possibly its greatest proponent and the German philosopher Immanuel Kant. Yet, these two thinkers interpreted idealism in very different ways. Kant described his brand of idealism as transcendent, whereas Berkeley called it 'immaterialism' which we today refer to as subjective materialism.

George Berkeley was of the opinion that the material world exists because there is a mind to perceive it and that things which are not within the conceptual framework of the human mind cannot be deemed real. He does not deny that objects exist, but that their existence on the physical realm is as long as there is a mind to perceive them. He summarized this in a famous Latin phrase 'Esse est percipi' (to be is to be perceived).

Immanuel Kant built his philosophical arguments as a refutation to David Hume and his theory of skepticism, that men cannot perceive causality as we only rely on experience to guide us in life. Kant proposed a philosophy where he said that reality exists independently of human minds but its knowledge is inherently unknowable to man because of sensory filters in our consciousness. These filters hamper our ability to see the 'thing in itself' - the Ding an sich - and thus our ultimate perception of things is always through the mind's fixed frame of reference.
Realism: Philosophy and Proponents
We can evade reality, but we cannot evade the consequences of evading reality. ~ Ayn Rand
Reality is that which, when you stop believing in it, doesn't go away. ~ Philip K. Dick
In the philosophical sense, realism postulates that reality exists in independence with human perception and is not dependent on observers to define its objective boundaries. To understand philosophical realism we must again turn to that giant of ancient philosophy and the father of the modern one - Plato. It may be confusing but his Theory of Forms, sometimes also referred to as Platonic Idealism, is the basis for realism, since it attempts to define the universal forms or simply 'universals'. A universal is the singular property of an object or thing which can exist simultaneously in two places in the same space-time continuum. This can be explained by the property of color, such as blue. The blueness of an object exists independently of the object itself in different locations. This is the problem of universals. How does one understand these 'Forms'? Plato thought they existed in a plane which did not come in direct contact with ours, we cannot feel or touch them, and that the laws of space-time did not apply to universals, yet they exist and by a natural or non-mental conception also provide structure to reality itself.

Modern realism has various forms such as, scientific, sociopolitical, aesthetic, epistemological and moral realism. It follows the general rejection of philosophical idealism and the acceptance of reality as independent of human perception. Aristotle is considered to be the foremost proponent of realism and, as Plato's student, had his philosophical beginnings rooted in Platonic idealism, yet developed his own theories regarding the nature of reality later on. Aristotelian realism proposes that ideas can free float without having matter, whereas matter cannot exist without some semblance of form, and this form is independent of mental cognizance.

Religious realism was put forth by Thomas Aquinas in the 13th century stating that true reasoning lies with the supreme reasoner - God - and that by aligning our rational reasoning minds with his tenets, we too can understand the universe and the nature of reality.

In more modern times philosophers such as Francis Bacon, John Locke and later G.E. Moore and Ayn Rand forwarded theories relating to moral realism. Whereas German theoreticians like Otto Von Bismarck and Carl Von Clausewitz were proponents of political realism.
Idealism vs. Realism
The definitions of these two philosophical doctrines reveal the dichotomy between their viewpoints and the resulting arguments that would necessarily arise out of a debate between the two. Idealists are of the opinion that the world, and everything in it, is but a creation of our minds and there is no objective reality. Realists counter this with a simple question - What if a man is tied to a time bomb and given the abort switch? What should he do? If he were an idealist, would he say that the reality of his situation is an imaginary one? That all this was happening as a result of his perception? Or, would he flick the switch and save his life, thereby admitting that the laws of physics are real and very much, affect human beings? It is a conundrum in which many an idealist has fallen. No one seems to have blown up though. Another poignant argument is the tree-falling-in-the-woods. What if a tree falls deep in the forest and there is no one to see or hear it? Has the tree then fallen? Or does it merely appear to us as fallen once we observe its predicament in relation to our own spatiotemporal reality? For an idealist, the tree doesn't exist as he has not observed it, the fact of its falling is beyond the realm of his mental cognition and therefore has not occurred. Yet we know this to be untrue. Observation is not the sole determinant of actuality and this is what realism offers, the independence of a material world removed from mental thought, but defined by 'universals'.

Idealists counter this argument with a very basic tenet of idealism, one that is attributed to George Berkeley. In showing how realism was an unthinkable concept, Berkeley postulates an assumption that every idea that is 'thinkable' is a concrete one. By this he means that concepts which can be grasped by the human mind with some measure of reason are true in form and exist. Therefore, since the idealist strapped to a bomb can conceptualize the imminent danger to himself, his reality is existential and he should take steps to save himself. The corollary for this is that only the definite concepts are the observable ones and not formless, independent concepts like the realists believe. So, a world outside this concrete 'thinkable' sphere can simply not exist. As man can only observe the ideas, concepts, and objects which are defined, and within his frame of reference. If this is the principle basis of realism, then realism as a concept itself is 'unthinkable'.

As we can see, the argument is between ideas and the laws of nature. Realists accuse idealists of being arrogant to the point of assuming that reality is but a creation of their corporeal minds, why then is the human mind the only one capable of this feat? Why have we been favored with this singular distinction? Possibly the best argument against idealism is Darwin's Theory of Evolution. It makes it very clear that reality existed in form and matter much before the mind of man evolved to an extent where it could hypothesize about the nature of the world. It is an absolute refutation of the principles of idealism as they stand.
Modern philosophy evolved from the theories of Berkeley and Kant to the more realism-oriented philosophy of existentialism. Thinkers like Søren Kierkegaard, the Russian writer Fyodor Dostoyevsky, and the fathers of post modernism, Friedrich Nietzsche and Jean-Paul Sartre have all focused on the human 'experience' of living, the importance of authenticity and the inability of traditional philosophies to effectively explain abstract ideas. Idealism can today be found in essays, where the writer has the freedom to explore metaphysical concepts without certain caustic determinants we call 'truth' or 'practicality'. Realism, on the other hand, is much more in touch with the human condition.