The proposal that reason gives humanity a special position in nature has been argued to be a defining characteristic of western philosophy and later western modern science, starting with classical Greece. Philosophy can be described as a way of life based upon reason, and in the other direction reason has been one of the major subjects of philosophical discussion since ancient times. Reason is often said to be reflexive, or “self-correcting,” and the critique of reason has been a persistent theme in philosophy. It has been defined in different ways, at different times, by different thinkers.
For many classical philosophers, nature was understood teleologically, meaning that every type of thing had a definitive purpose which fit within a natural order that was itself understood to have aims. Perhaps starting with Pythagoras or Heraclitus, the cosmos is even said to have reason. Reason, by this account, is not just one characteristic that humans happen to have, and that influences happiness amongst other characteristics. Reason was considered of higher stature than other characteristics of human nature, such as sociability, because it something humans share with nature itself, linking an apparently immortal part of the human mind with the divine order of the cosmos itself. Within the human mind or soul (psyche), reason was described by Plato as being the natural monarch that should rule over the other parts, such as spiritedness (thumos) and the emotions. Aristotle, Plato’s student, defined human beings as rational animals, emphasizing reason as a characteristic of human nature. He defined the highest human happiness or well-being (eudaimonia) as a life which is lived consistently, excellently and completely in accordance with reason.
The conclusions to be drawn from the discussions of Aristotle and Plato on this matter are amongst the most debated in the history of philosophy. But teleological accounts such as Aristotle’s were highly influential for those who attempt to explain reason in a way that is consistent with monotheism and the immortality and divinity of the human soul. For example, in the neo-platonist account of Plotinus, the cosmos has one should, which is the seat of all reason, and souls of all individual humans are part of this soul. Reason is for Plotinus both the provider of form to materials things, and the light that brings individuals souls back into line with their source. Such neo-Platonist accounts for the rational part of the human soul were standard amongst medieval Islamic philosophers, and under this influence, mainly via Averroes, came to be debated seriously in Europe until well into the renaissance, and they remain important in Iranian philosophy.
The early modern era was marked by a number of significant changes in the understanding of reason, starting in Europe. One of the most important of these changes involved a change in the metaphysical understanding of human beings. Scientists and philosophers began to question the teleological understanding of the world. Nature was no longer assumed to be human-like, with its own aims or reason, and human nature was no longer assumed to work according to anything other than the same “laws of nature” which affect inanimate things. This new understanding eventually displaced the previous world view that derived from a spiritual understanding of the universe.
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