Ancient
Plato distinguishes between noesis and dianoia. Noesis as the "intuitive seeing of ideas" refers here to the ability to recognize the being in its essence, while dianoia means the conceptual, methodical-discursive way of knowledge.
Aristotle determined reason on two levels. On the one hand the thinking reason, the logos, which is a conversation with itself, and on the other hand the action-directing reason, the phronesis, which is directed towards practice. There is a direct relationship between phronesis and logos (EN VI 5, 1140 b20) The logos determines rational action when it serves to grasp the median of virtue (see Mesotes) Man is not only a communal being (zoon politikon), but also a rational being (zoon logon echon) (Pol. I 2, 1253 a1-18) As it was for Heraclitus or Anaxagoras, Aristotle regarded the nous as a general, unchanging world principle. "Anaxagoras is right when he calls the spirit (nous) that which cannot be affected and is unmixed, precisely because he posits it as the principle (arché) of motion. For only on this condition can he move as the unmoved and rule as the unmixed." (Physics 5, 256 b24 f)
In the Stoa, reason served to regulate the bodily drives and thus to arrive at a balanced, virtuous life. Man is part of nature and the task of reason is to fit life into the cosmic order (logos). Reason cannot go against the order of nature. Thus, Cicero asks, "Is anything natural that happens against reason (ratio)?" (Conversations in Tusculum, 4th book, 79 f.). In Seneca the answer is found: "Nature, in fact, must be taken as a guide: she pays attention to reason (ratio), and the latter asks her advice."
European Middle Ages
The Latin terminology translated noesis with intellectus and dianoia with ratio. The philosophy of the Middle Ages was characterized in its beginnings by the idea of an integration of religion and philosophy. The two were not supposed to contradict each other. An important pioneer in this respect was Augustine of Hippo: "There are two different remedies which must be applied in succession, namely authority and reason. Authority demands faith and prepares man for reason. Reason leads to insight and knowledge. Yet even authority is not wholly abandoned by reason, since it is necessary to consider whom to believe, and no less does undoubted supreme authority attach to truth already plausible and recognized." It is no longer nature, as in the Stoa, but a transcendent divine will, as in Neoplatonism, which is the standard for human action. "The first ruin of the rational soul is the will to do what the highest and innermost truth forbids. Consequently man was cast out of Paradise into our earthly world, and thus passed from eternity into temporality, from abundance into want, from strength into weakness, but not from essentially good to essentially bad. For no being is bad."
In the Middle Ages, however, God was also thought of as an authority superior to all human thought, with Peter Damiani even going so far as to say that thought has its origin in the devil and is not valid before God. Accordingly, he held that philosophy was the "handmaiden of theology".
Thomas Aquinas, on the other hand, thought it necessary that the knowledge of the world should not be founded on errors, because this would endanger right faith in God. "It is evident, then, that the opinion of certain people is wrong who say that it does not matter for the truth of faith what one thinks about creatures, if one has the right opinion only with regard to God [...] for error about creatures passes over into a wrong opinion of God, and leads men's minds away from God, to whom faith nevertheless seeks to direct them, in that error subordinates creatures to other causes." (ScG II 3 n. 864). For Thomas, action that yields to unreasonable impulses is bad. "Any volition that departs from reason, whether this be right or wrong, is always bad." (STh I/II 19 a.5)
In the High Scholasticism developed the striving to separate beliefs and reason again. Important representatives of this development were John Duns Scotus and William of Ockham. Meister Eckhart and Martin Luther again equated intellectus with understanding and ratio with reason, whereby understanding (intellectus/noesis) as the knowledge of essence was superior to reason (ratio/dianoia), which operated discursively and argumentatively.
Non-European Philosophy
Similar approaches can be found in almost all cultural circles. In the Islamic tradition, the influential philosopher Avicenna described reason as a constant emanation of God. Eastern wisdom teachings such as Yoga and Zen teach the limits and contradictions of reason and how to free oneself from them.
Nicholas of Cusa
Nicholas of Cusa emphasized that reason is a special faculty of man, which can only develop its power through education. "Man, as man, relates to the animal as a learned man to an unlearned man. For the learned sees the letters of the alphabet (litteras alphabeti) and so does the unlearned. But the learned man forms syllables (syllabas) by various combinations of the letters, and words from syllables, and sentences from these. The unlearned cannot do this, because he lacks the art which the learned has acquired by training his reason (ab exercitato intellectu). Man, then, by the power of his reason, is able to assemble and separate the natural images of knowledge (species naturales) and to create from them images of knowledge and signs of knowledge of reason and art. By this man excels the animals, and the learned the unlearned, because he has a trained and educated reason (exercitatum et reformatum intellectum)."
For Cusanus, as later for Kant, reason is the highest level in the triad of senses - understanding - reason. While the understanding summarizes the manifold sensory impressions, the insight of reason in the vision of the higher still goes beyond the understanding. Following Raimundus Llullus, he described the unity of reason itself as the simplest synopsis of the whole as a triad of (1) the knower, (2) the known, and (3) the process of knowing. Intellect transcends ratio insofar as it forms a unity out of what is discursively separate in ratio (intelligens, intelligibile, intelligere). This trinity of (1) indivisibility (indivisio), (2) distinction (discretio), and (3) connection (conexio) refers to the category theory in Charles S. Peirce and the process philosophy in Alfred North Whitehead, in his category of the elementary (see Process and Reality). The unity of reason is the coincidence of opposites (Coincidentia oppositorum). Like reason, however, reason is limited. The essence of God as light, which comes to meet it, remains closed to it. "Therefore reason moves toward wisdom as its proper life. And sweet it is for every spirit to ascend continually to the source of life, however inaccessible it may be. [...] As when a man loves something because it is lovable, he rejoices that in that which is lovable there are to be found infinite and inexpressible reasons for love."
Rec
→ Main article: Enlightenment
The European Age of Enlightenment is driven by the idea that reason is capable of bringing truth to light. The religion of reason is supposed to overcome the dogmatic oppression and authoritarianism of the Christian religion and bring freedom and prosperity to all. Thus, rationalism saw reason as "pure," that is, as cognition independent of empirical experience, which formed the basis of philosophical systems in Descartes, Spinoza, and Leibniz. The concept of human reason has often been equated with consciousness, self-consciousness, or mind. In rationalism, reason represents the central element of the cognitive process. According to it, deductive knowledge is possible with it, which can be achieved even without sensual perceptions. In contrast, empiricism (e.g. David Hume) denies the possibility of knowledge a priori, i.e. without experience.
Kant
At the end of the 18th century, Immanuel Kant brought together the approaches of rationalism and empiricism in his critical philosophy. With Kant, reason finally gained its significance as the higher principle of cognition compared to understanding. He defined reason as the aposterior cognitive faculty bound to sensory impressions. With reason he distinguished between ("pure") theoretical and practical reason. According to Kant, theoretical reason is the ability to draw conclusions, to examine oneself and to arrive at a priori ideas of reason (soul, God, world) independently of experience. In his work Critique of Pure Reason, Kant tries above all to show the limits and the conditionality of human reason. In this way, the concept of reason could be freed from metaphysical speculation and the way paved for a scientific metaphysics. Kant thus made a major contribution to the main methods practiced in science today, in which theory development and empirical experimentation are mutually pursued. Practical reason, on the other hand, according to Kant, refers to the setting of ethical principles to which the will is subjected and which thus justify and guide action individually and socially. At the beginning of the preface to the 1st edition of the Critique of Pure Reason it states:
"Human reason has the peculiar fate in one genus of its knowledge: that it is harassed by questions which it cannot dismiss; for they are given up to it by the nature of reason itself, but which it cannot answer either; for they exceed all the capacity of human reason."
Hegel
After Kant had described the limits of knowledge and reason, some representatives of German idealism did not want to accept them. Hegel explicitly recognizes Kant's insight of reason as the ground (substance) of freedom. But he calls Kant's position subjective because he only allows the subject to know true appearances from things and not these themselves as they are in themselves. To get beyond this, absolute reason is needed. For him, it is the speculative capacity to comprehend the Absolute in the movement of all its moments. For him, it is the unity- and meaning-giving ground that eternally goes out of itself, thus dividing itself by realizing (or materializing) itself in the course of history in ever new appearances as (time-)spirit and nature, falling back into unity and thus "returning to (or into) itself." Hegel says that because it takes everything back into itself and brings it into its form (unity), that is, because it basically has no limit, it is infinite, and because it only knows itself, absolute. The absolute itself is for him God, the absolute spirit. To know him is for Hegel the supreme goal of all philosophy. The connection of reason with the process of history has subsequently had a very clear effect, especially through Marxism. Reason and progress (economic, scientific, technical, social) have since been closely linked in their social significance. The idea of freedom of reason from the Enlightenment, on the other hand, has been largely suppressed.
Schopenhauer
Arthur Schopenhauer distinguishes between understanding as the ability to perceive visually and reason as the ability to perceive abstractly and discursively. He regards reason as specifically human, whereas understanding also belongs to (higher) animals. These are in part even able to grasp multi-level causal connections intellectually, but cannot think rationally because they lack abstract concepts and ideas.
Modern
In view of the horrors of the 20th century (Holocaust, imperialism), in which they also saw a connection with industrialization, a critique of rationality was elaborated by the members of the Frankfurt School. It criticizes the modern scientific establishment and its faith in facts, which is determined by positivism. Reason and understanding, it argues, have become instruments for the oppression of the individual and have all but stifled the "self-liberating powers" of reason. Jürgen Habermas contrasts "instrumental reason" (Theodor W. Adorno, Max Horkheimer) with the intersubjective "communicative reason" of the life world, which is based on freedom from domination and violence and mutual recognition. What is needed is a new stage of enlightenment, which - according to Habermas - is not yet complete.
In his thirteenth encyclical Fides et ratio in 1998, Pope John Paul II addressed the tension between reason and faith from the perspective of the Roman Catholic Church. Pope Benedict XVI took up the thoughts of his predecessor in his speech at the University of Regensburg on 12 September 2006 and in his statements on the Catholic Church's image of God.
