Descartes, Marx, Aristotle and Plato: Core Philosophical Ideas Explained

Descartes

Truth is only attained through doubt. Doubt everything that is not clear. This is the method.

• Sensation, dreams and illusion can deceive us. Reason, however, leads to certainty: since we doubt, we must think, and so the first truth is cogito, ergo sum (I think, therefore I am).
• A thinking being cannot prove the existence of the world on its own, because it has already placed everything in doubt. It is necessary to prove the existence of God. If God exists, He is infinitely good and would not want to deceive us about the existence of the world. If I am finite and I know that the infinite exists, that idea can only have been placed in me by God.
• If God exists, the third truth follows: the world exists.

The first truth establishes the thinking substance (res cogitans). The second establishes God as infinite substance (res infinita). The third establishes the world as extended substance (res extensa), whose essence is geometric.

The main problem is uniting res cogitans and res extensa. He speaks of the existence of a gland in the neck that connects the body to the soul.

Marx

The essence of humankind is work. The history of humankind is the history of work (historical materialism).

• In the Middle Ages, the mode of agricultural production and the relations of production were dichotomous: noble and serf.
• In modern times, the mode of industrial production and the relations of production are dichotomous: capitalist and worker.
• The mode of production is the infrastructure. Each epoch has an infrastructure and a superstructure (art, religion), which serves to maintain the privileged position of the masters. The infrastructure determines the superstructure.

Each historical period has its class struggle. This is named dialectical materialism. Each historical period has its own internal contradiction. In modern times, the fall of power of the nobility, through the rise of the servants, gave way to the struggle of classes, which is the engine of history. Marx says that the end is communism. Without class struggle, dialectics and historical change would be eliminated.

Aristotle

Metaphysics is being insofar as it is being. Being can be said in many ways (categories). There are 10 categories of existence. The first and most important is substance (concrete, individual reality). A dog is followed by accidents that describe it: quantity 3 years, quality, relation company of its owner, action eating and walking, place garden.

If we want to define substance, we refer to the genus and the specific difference (form). Aristotle divides substance into matter and form. Matter is the principle of the individual subject. Form is the manner in which matter is ordered, and it determines what the substance is (genus and species). Metaphysics is more general and complex.

Aristotle explains the problem of motion through act and potency (rejecting Parmenides). Potency is possibility; act is the actualization of being. Motion and change are explained by the passage from potency to act. He distinguishes three types: place, growth and alteration.

Plato

Plato formulated the theory of Ideas in order to overcome the contradictions of Parmenides and Heraclitus. He accepted, like Heraclitus, that the world is in constant change and decay, so there can be no science of what is in change; knowledge cannot rest on sensible objects. He says there is a world of intelligibility, formed by Ideas. There are two worlds:

• The world in which we live, with material beings. The sensible world is characterized by imperfection. It is the shadow of the other world, the perfect world of Ideas (beauty, goodness, etc.). These beings can only be grasped by reason, the noblest part of the soul.

By distinguishing between these two types of worlds, Plato defines an ontological dualism. The Ideas (which he also calls Forms) are real objects that exist independently of things and independently of our thinking. The sensible world participates in the Ideas. Ideas are real, and the sensible is appearance. Ideas are equal, have the character of being: unique, eternal, immutable and sublime. Things are sensible, multiple and subject to change, so they are less real than Ideas. Plato says that immutable notions belong to the intelligible world, where all Ideas are. (The idea of a circle: an imperfect circle exists in the world, but the perfect circle is in the world of Ideas.) The Idea of the Good is the maximum Idea for Plato.