Idealism is a philosophical current that defends that the existence of things in the world depends on ideas present in the human spirit.
For idealistic philosophers, reality is known through these ideas. In other words, human beings' contact with the world is mediated by ideas. Objects, on the other hand, have something that goes beyond their appearance or the way they are perceived.
Thus, for idealism, the external world (everything that exists outside of us) depends on the "I", also called the subject or consciousness.
Platonic Idealism
Plato's theory of ideas inaugurates idealism from the separation between the sensible world and the ideal world. For him, everything that can be perceived through the senses is nothing more than an imitation of an idea.
In the cave allegory, Plato states that the senses are flawed and lead human beings to a life of ignorance, attached to appearances, represented by the shadows projected at the bottom of the cave.
For him, true knowledge would be in the use of reason, the only tool to achieve true knowledge, knowledge of ideas.
German Idealism
The philosophical approach to idealism in Germany is taken up by Immanuel Kant (1724 - 1804). It starts in the 80s of the 18th century and extends into the first half of the 19th century.
For Kant, the limits of human reason prevent one from knowing things as they really are, the thing-in-itself, but one can only conceive how these things manifest in the world, how they appear to us and how we interpret.
Kantian idealism is an attempt to unite two opposing currents: rationalism and empiricism.
From the 19th century onwards, German idealism was approached by a group of philosophers called post-Kantians. They were Johann Gottlieb Fichte (1762 - 1814), Friedrich Wilhelm Joseph von Schelling (1775 - 1854) and Georg Wilhelm Friedrich Hegel (1770 - 1831).
In the German idealist doctrine, the Kantian "thing-in-itself" is abandoned and the power of reason is reinforced to show reality as something absolute and an object of reflection.
Transcendental Idealism
Kant's transcendental idealism is founded on the fact that knowledge does not result from a neutral experience.
Kant claims that the "thing-in-itself" is unknowable (cannot be known) and what can be known are its representations in the world.
Hegelian Idealism
Hegel's idealism is understood as absolute idealism. The thinker affirms that the transformation of reason and its contents is driven by reason itself.
For Hegel, the world is an idea, as is everything in it.
Materialism
It is a philosophical current that defends existence only through what is materially manifested. In this line of thought, existence can only be explained in material perspective.
O materialism states that the cause and effect relationships (causal relationships) exist only in matter and not in ideas, as defended by idealism.
