Hume vs Descartes: Rationalism and Empiricism Compared
Hume's Critique of Rationalist Philosophy
David Hume’s philosophy is deeply connected to René Descartes, primarily through his rigorous critique of the main premises of rationalism.
The Problem of Inductive and Deductive Methods
First, Hume criticizes the methodology of knowledge. He identifies two primary types of methods:
- The Inductive Method: Using particular cases to develop a general law.
- The Deductive Method: Deriving individual cases from a general statement.
Regarding the deductive method, Hume criticizes rationalists for basing their systems on principles that stem from innate ideas to develop knowledge. Hume, like all empiricists, rejects the existence of innate ideas and, therefore, the validity of the deductive method for discovering truths about the world.
The problem with the inductive method is that there is nothing that allows us to move from particular cases to a general statement with absolute certainty, because we can never be sure that a future case will not invalidate the general law.
Causality, Substance, and the Limits of Understanding
Hume criticizes the principle of causality (the belief that everything that begins to exist has a cause for its existence). According to him, what we perceive as the cause of something is simply a product of the understanding. One cannot observe cause and effect directly, but only one event following another as a matter of habit. Similarly, one cannot prove the idea of necessity.
He argues that the idea of substance is also a product of the understanding and criticizes the specific use Descartes makes of this concept.
Primary and Secondary Qualities
Descartes believed that secondary qualities (such as color and texture) are merely subjective perceptions of our mind. However, Hume argued that if secondary qualities are subjective, primary qualities cannot be objective either, since our knowledge of the primary stems directly from the secondary.
The Impossibility of Proving God and the Self
Hume denies the possibility of proving the existence or non-existence of God, because such demonstrations are of a causal nature, which he has already challenged. Furthermore, Hume criticizes the Cartesian thinking substance (the cogito). While Descartes suggests that the process of doubt implies a stable consciousness, Hume argues that we only have perceptions of consciousness; therefore, we cannot prove the existence of a permanent self.
The Rejection of Metaphysics
Finally, Hume criticizes the very foundation of metaphysics. If we understand metaphysics as the knowledge that attempts to explain the essence of things to reach ultimate reality, it faces two problems:
- It cannot be derived from impressions of sensation, and therefore, impressions of reflection cannot have objective value.
- Strict knowledge of reality is impossible.
In the end, Hume concludes that it is impossible to rationally substantiate absolute knowledge.
Descartes on Doubt and the Search for Truth
The Role of Methodical Doubt
According to Descartes, doubt is something that prevents one from seeing evidence, as it leads to confusion. The uncertainty caused by doubt leads a person to withhold judgment on the truth or falsity of a statement until there is reasonable evidence to prove it.
Descartes employs methodical doubt to find certainty. To do this, he doubts everything until he finds something that is impossible to doubt, thereby establishing a foundation of certainty.
Defining Truth as Certainty
Descartes understands truth as certainty. This assurance is achieved by verifying that a judgment is clear (manifested without difficulty) and distinct (not to be confused with other judgments). To reach this certainty or truth, Descartes utilizes mathematics, starting from simple deductions and moving through the development of more complex elements.