I am currently reading The Closing of the Western Mind which charts how the reason and rationality of the Greek world was replaced with the dogma of faith in the Medieval world. The interfaces of rationality are fascinating; I recently read through A World Lit Only By Fire which looked at the Medieval mind and how it changed with the reformation and renaissance. I also finished Peter Watson's The Modern Mind which looks a the rationality of the twentieth century and how science came to dominate modern intellectualism. The rationality of humankind is an amazing thing.
John Barrdear : Without necessarily advocating his thesis, it might be interesting to compare with John Ralston Saul's "Voltaire's Bastards: The Dictatorship of Reason in the West". Wikipedia's surprisingly brief one-paragraph summary really is a one-paragraph summary:

These books deal with themes such as the dictatorship of reason unbalanced by other human qualities, how it can be used for any ends especially in a directionless state that rewards the pursuit of power for power's sake. He argues that this leads to deformations of thought such as ideology promoted as truth; the rational but anti-democratic structures of corporatism, by which he means the worship of small groups; and the use of language and expertise to mask a practical understanding of the harm this causes, and what else our society might do. He argues that the rise of individualism with no regard for the role of society has not created greater individual autonomy and self-determination, as was once hoped, but isolation and alienation. He calls for a pursuit of a more humanist ideal in which reason is balanced with other human mental capacities such as common sense, ethics, intuition, creativity, and memory, for the sake of the common good, and he discusses the importance of unfettered language and practical democracy.

cam : The Greeks recognised that rhetoric didnt need a moral rudder to be presuasive which is why Aristotle came up with the Philosopher King - a moral, learned individual able to rule in the public good.

It is probably also why liberalism's utilitarianism tries to temper it with morality and personal responsibility. That is where the social good comes in.
In The Medieval Mind, William Manchester charts the rationality of the medieval period and how it clashed and ultimately fell prey to the new rationality of reason with the Reniassance.

The medieval rationality was predicated on certainty. The scriptures were perfect and could guide the individual in both life and death. This gave the Pope in Rome absolute power and the politics of the christian kingdoms in Germany (Holy Roman Empire), England, France, Spain and Portugal followed the politics of Rome. The grace of the Pope could be politically positive but Rome's ire could be equally negative, often with the threat of excommunication.

The monarchs and Bishops were egotistic oddities. The medieval person was not an individual and was not imbued with an ego. The architects and builders of the great cathedrals are anonymous; even more so as they were often built across up to thirty generations of workers. They were glorfying God, not themselves.

Peasants did not carry names beyond Hans, Jacques, or Carlos. Their world was intimately familiar and small - not extending beyond the terrifying boundary of the village. It was a violent world both internally and externally. Manchester writes:

In the medieval mind there was also no awareness of time, which is even more difficult to grasp [than the lack of ego]. Inhabitants of the twentieth century are instinctively aware of past, present and future. ... In all Christendom there was no such thing as a watch, clock or calendar. Generations succeeded one another in a meaningless, timeless blur.

As an example I can remember my grandfather saying he saw his first car in 1911 when he was a kid in Helensburgh, NSW and that it had a gas bag on its roof. In the next sentence he said he saw a man on the moon in 1969. I can even claim to having the internet change modern life in my small time on this earth; but someone born in 791 would live the exact same life as someone born in 991. It is no wonder that we cannot understand the timelessness and static nature of life in the Dark Ages and Medieval period. Manchester continues:

Any innovation was inconceivable; to suggest the possibility of one would have invited suspicion, and because the accused were guilty until they proved themselves innocent by surviving impossible ordeals - by fire, water, or combat - to be suspect was to be doomed.

The Christendom of the Medieval period was built on the rituals of paganism. However, ironically the Renaissance also came back to the fore by rediscovering and disseminating the learnings and teachings of the pagan civilizations prior to European Christendom; namely Greek and Roman which had been libraried by the Muslim world.

Before reason could replace dogma and certainty the political power of Rome had to be broken. It was long known that Rome and the papalcy was depraved, corrupt and given to every sin and vice known to humankind. The Church was a hotbed of simonism, debauchery and arbitrary vengeance.

It was the increasing power of the rising nation-states of England and German which provided protection for the outspoken critics of the Papalcy. England was sufficiently remote and wealthy enough that it could protect Erasmus who pillorised the depravity of the Holy See to the amusement and nodding heads of all Europe.

The Holy Roman Empire was also converting to the modern Germanic nation and was able to provide political protection to Martin Luthar when he had a run in with the elixor-like salesman Johann Tetzel who would sell 'letters of remission' that would forgive anything in the Pope's name for a price.

It helped that when England and Germany broke with Rome they quickly confiscated the existing Catholic properties inside their nations; increasing their own wealth immeasureably.

Utlimately though it was reason that shook faith. The nature of the scientific mind is that everything is temporal and any theory is only as good until another comes along that is more accurate. This is in complete contrast to the medieval mind which is largely static and secure in the dogma of the unchanging world being a reflection of God's perfectibility.

Rationality changes mean that an individual from another period cannot understand ours, just as we cannot understand theirs. To be without ego and time in a liberal democratic market economy is unfathomable just as the unchanging permanence and certainty of the Medieval period would be inconceivable to us.
adam : I remember being struck in some random German museum by a sense of how filled with symbolic meaning each act of a medieval life could be. There was a catalogue of medieval social symbology, eg putting a belt on a child meant you were becoming their guardian, standing under x was for weddings, etc etc. There was a massive list of them and I had this sudden sense of living in a way where every action had a social consequence ...

Now I'm not a scholar of the period so perhaps I am exaggerating my own personal response. But it does make it easier to explain how eg Umberto Eco could transition so easily from a medievalist into semiotics - because so much of the medieval world is all about interpreting shared cultural symbols.
cam : It was interesting how conservative the change over to christianity from paganism was. The church allowed people adopting christianity to continue the same rituals from paganism just in the name of christ or with catholic (or the competing christianity versions from Constantinople times) approval. The glory to changed just not the ritual. That was true of medieval times which was largely superstitious still.
adam : Amazing how patient you can be when you think of time in seasons I guess ...
cam : Heh good point. I am having all sorts of problems getting used to Hawaiin time here. They are just slow. It was the same when I moved from NY to Virginia. Virginian time was an order of magnitude less than NY time. Wonder if the medieval mind was imbued with great patience.
Cam Riley: South Sea Republic. Freedom, liberty, equity and an Australian Republic.