Descartes, Kant, and Hume: Philosophical Inquiries
Descartes’s Philosophy
The Existence of God
To prove God’s existence, Descartes examined his conscience and the concept of perfection and infinity. God, to him, represents perfection and infinity.
Descartes defined God as a perfect, immutable, infinite substance—the supreme unifying point towards which all things tend. This God is the cause and preserver of all beings, the creator and author of nature, and the guarantor of our innate ideas. All created beings strive towards this supreme unity.
God is the creator and preserver of the world, the author of nature and its immutable laws. This is Descartes’s idea of God: all-seeing, perfect, and the ultimate aspiration of every human.
The External World
Inspired by the success of mathematics and the new sciences, Descartes embarked on a new philosophical path. He believed that human subjectivity is the source of certainty and the key to unlocking knowledge and dominating nature. He prioritized understanding how reason represents things, relations, and order, rather than simply asking what things are.
Descartes believed that reason is universal in two ways: it is common to all humans, and external reality is governed by rational laws. He saw mathematics as a part of a larger rational order. He believed that if a universal rational order exists, a universal science with a single method should be possible, with mathematics as its foundation.
Descartes’s first certainty was “I think, therefore I am”—the existence of himself as a thinking substance (res cogitans). From this, he deduced the existence of God (res infinita), and from God’s existence, he deduced the existence of the world (res extensa). God guarantees that reason functions correctly when used methodically and that the world exists.
A Mechanistic World
Descartes’s scientific project had two methodological approaches. First, he sought to establish the general principles of reality, explaining things from their true causes and deriving their effects. Second, he emphasized observation and testing of concrete phenomena to support the truth of universal propositions. This latter concept reflects an empiricist stance, highlighting the importance of experience in explaining natural phenomena. His focus was on the principles of material things, the Cartesian theory of bodies, and the constitution of the natural world.
Kant
Origin and Modes of Knowledge
All mental content originates from perceptions—immediate experiences, feelings, and emotions. We form ideas, which are copies of impressions with varying degrees of force. Complex ideas are sets of simple perceptions. Every simple impression has a corresponding simple idea, and every simple idea has a corresponding sense impression or reflection.
At birth, the human mind is a blank slate. Hume distinguishes between impressions and ideas as elements of knowledge and introduces two types of knowledge:
- Knowledge of Relationships Between Ideas: This includes propositions of geometry, algebra, and arithmetic. These propositions affirm relationships between ideas and are reached through reasoning without experience. Their truth is independent of experience; they are certain because their opposites are impossible, implying contradictions. They are necessary propositions, empty of empirical content. For example, 2 + 2 = 4, or a triangle has three sides.
- Knowledge of Facts: These propositions relate to events and are wholly dependent on experience. Experience guarantees their truth, as the opposite of any fact is always possible and implies no contradiction. These propositions are contingent. For example, “Tomorrow the sun will rise” is no less intelligible than “Tomorrow the sun will not rise.”