Immanuel Kant in the context of "Age of Enlightenment"

German philosophy, meaning philosophy in the German language or philosophy by German people, in its diversity, is fundamental for both the analytic and continental traditions. It covers figures such as Gottfried Wilhelm Leibniz, Immanuel Kant, Georg Wilhelm Friedrich Hegel, Karl Marx, Friedrich Nietzsche, Martin Heidegger, Ludwig Wittgenstein, the Vienna Circle, and the Frankfurt School, who now count among the most famous and studied philosophers of all time. They are central to major philosophical movements such as rationalism, German idealism, Romanticism, dialectical materialism, existentialism, phenomenology, hermeneutics, logical positivism, and critical theory. The Danish philosopher Søren Kierkegaard is often also included in surveys of German philosophy due to his extensive engagement with German thinkers.

Christian Wolff (/vɔːlf/; less correctly Wolf, German: [vɔlf]; also known as Wolfius; ennobled as Christian Freiherr von Wolff in 1745; 24 January 1679 – 9 April 1754) was a German philosopher. Wolff is characterized as one of the most eminent German philosophers between Leibniz and Kant. His life work spanned almost every scholarly subject of his time, displayed and unfolded according to his demonstrative-deductive, mathematical method, which some deem the peak of Enlightenment rationality in Germany.

Wolff wrote in German as his primary language of scholarly instruction and research, although he did translate his works into Latin for his transnational European audience. A founding father of, among other fields, economics and public administration as academic disciplines, he concentrated especially in these fields, giving advice on practical matters to people in government, and stressing the professional nature of university education.

Arthur Schopenhauer (/ˈʃoʊpənhaʊər/ SHOH-pən-how-ər; German: [ˈaʁtuːɐ̯ ˈʃoːpn̩haʊɐ] ; 22 February 1788 – 21 September 1860) was a German philosopher. He is known for his 1818 work The World as Will and Representation (expanded in 1844), which characterizes the phenomenal world as the manifestation of a blind and irrational noumenal will. Building on the transcendental idealism of Immanuel Kant, Schopenhauer developed an atheistic metaphysical and ethical system that rejected the contemporaneous ideas of German idealism.

Schopenhauer was among the first philosophers in the Western tradition to share and affirm significant tenets of Indian philosophy, such as asceticism, denial of the self, and the notion of the world-as-appearance. His work has been described as an exemplary manifestation of philosophical pessimism. Though his work failed to garner substantial attention during his lifetime, he had a posthumous impact across various disciplines, including philosophy, literature, and science. His writing on aesthetics, morality and psychology has influenced many thinkers and artists.

A phenomenon (pl. phenomena), sometimes spelled phaenomenon, is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which cannot be directly observed. Kant was heavily influenced by Gottfried Wilhelm Leibniz in this part of his philosophy, in which phenomenon and noumenon serve as interrelated technical terms. Far predating this, the ancient Greek Pyrrhonist philosopher Sextus Empiricus also used phenomenon and noumenon as interrelated technical terms.

An unobservable (also called impalpable) is an entity whose existence, nature, properties, qualities or relations are not directly observable by humans. In philosophy of science, typical examples of "unobservables" are the force of gravity, causation and beliefs or desires. The distinction between observable and unobservable plays a central role in Immanuel Kant's distinction between noumena and phenomena as well as in John Locke's distinction between primary and secondary qualities. There is considerable disagreement about which objects should be classified as unobservable, for example, whether bacteria studied using microscopes or positrons studied using cloud chambers count as unobservable. Different notions of unobservability have been formulated corresponding to different types of obstacles to their observation.

In aesthetics, the concept of taste has been the interest of philosophers such as Plato, Hume, and Kant. It is defined by the ability to make valid judgments about an object's aesthetic value. However, these judgments are deficient in objectivity, creating the 'paradox of taste'. The term 'taste' is used because these judgments are similarly made when one physically tastes food.

Criticism of Christianity has a long history that stretches back to the initial formation of the religion in the Roman Empire. Critics have challenged Christian beliefs and teachings, as well as actions taken in the name of the faith, from the Crusades to modern terrorism. The arguments against Christianity include claims that it is a faith of violence, corruption, superstition, polytheism, homophobia, bigotry, pontification, abuses of women's rights, and sectarianism.

In the early years of Christianity, the Neoplatonic philosopher Porphyry emerged as one of the major critics with his book Against the Christians, along with other writers like Celsus and Julian. Porphyry argued that Christianity was based on false prophecies that had not yet materialized. Following the adoption of Christianity by the Roman Empire, dissenting religious voices were gradually suppressed by both governmental and ecclesiastical authorities. Christianity has faced significant theological criticism from thinkers of other Abrahamic religions, particularly including Judaism and Islam. Notably, Maimonides, the renowned rabbi, Jewish philosopher, and Torah scholar of the 12th century, argued that Christian practices and doctrines constituted idolatry and deviated from the strict monotheism (shituf) of Jewish and Muslim theologies. Similarly, Islamic scholars have critiqued Christian beliefs about the Trinity and the divinity of Jesus, viewing these concepts as incompatible with the concept of monotheism. These critiques reflect deep theological disagreements rooted in their shared scriptural traditions and divergent doctrinal interpretations. A millennium later, the Protestant Reformation led to a fundamental split in European Christianity and rekindled critical voices about the Christian faith, both internally and externally. In the 18th century, deist philosophers such as Voltaire and Jean-Jacques Rousseau were critical of Christianity as a revealed religion. With the Age of Enlightenment, Christianity was criticized by major thinkers and philosophers, such as David Hume, Thomas Paine, and the Baron d'Holbach. The central theme of these critiques sought to negate the historical accuracy of the Christian Bible and focused on the perceived corruption of Christian religious authorities. Other thinkers, like Immanuel Kant, offered critiques of traditional arguments for the existence of God, while professing to defend Christian theology on novel grounds.