Descartes and Hume: Contrasting Views on Knowledge and Reality
Descartes’ Rationalism: Foundations of Knowledge
Methodical Doubt and the Cogito
Methodical doubt is applied to all knowledge, as all true knowledge must be differentiated from sleep. That which cannot be doubted is the fact that we think and the ability to do so.
The Existence of God
God is the guarantee of true knowledge. If the subject comes to understand and methodically assured knowledge, they can be sure that their thinking is real, since God cannot deceive us when we act with rationality.
The External World
The external world is the third of Descartes’ innate ideas. We may have wrong perceptions or fragments of the reality outside us, but we do not doubt that this reality exists.
Hume’s Empiricism: A Challenge to Rationalism
Hume’s Major Philosophical Works
- A Treatise of Human Nature: Reflecting on the criticism of Cartesianism regarding knowledge. A brief summary is found in the Abstract.
- An Enquiry Concerning the Principles of Morals: Focuses on emotivism.
Key Concepts in Hume’s Philosophy
- Association: Principles according to which ideas are related to form sets of knowledge.
- Causality: A necessary link between two phenomena, such that one is necessarily derived from the other.
- Knowledge: Security of having an idea linked to reality.
- Belief: An idea linked to an impression.
- Skepticism: Inability to accept an idea that is not validated by experience.
- Idea: A “secondary” perception, following an impression and registered in the mind.
- Mind: The place where various ideas are “represented.”
- Memory: A set of ideas that concentrate the mind on the basis of contiguity and interest.
- Reason: Hume does not understand reason as Descartes does (innate ideas), but more like an instinct that helps us discern actions in real life.
Hume’s Critique of Causality
The cause-effect relationship is the basis of our understanding of nature. However, the perceived necessity in this relationship is only an association of ideas based on the probability that a given fact will occur. It is merely a state of assumption. Hume refused Cartesianism for being too dogmatic and for its reliance on innate ideas. For Hume, the criterion for valid knowledge is the principle of copy: only an idea that comes from an impression is valid.
Hume’s Theory of Knowledge: Empiricism
Hume criticizes innate ideas, asserting that all our ideas and concepts come from perception and the senses. Perceptions are of two types:
- Impressions: Immediate, current, spontaneous.
- Ideas: Reflexes, images that become memories.
Knowledge, for Hume, gives confidence only when it comes from experience.
Matters of Fact vs. Relations of Ideas
- Matters of Fact: Based on the senses and cannot be subjected to pure logic. Only what is true can be proved or verified empirically.
- Relations of Ideas: Based on rules, calculations, or arguments inherent to their own language (e.g., mathematics, logic).
Hume’s Emotivist Ethics
Ethics, for Hume, has its origins in feelings. Individuals have no impressions or ideas on which to base our moral ideas, as most of our actions are targeted to serve the passions rather than abstract ideas.
Hume’s Critique of Cartesian Innate Ideas
The Self (Cogito)
Hume discusses Descartes’ “I” (Cogito) but does not deny personal existence; rather, he delves deeper. He denies that there is an immutable identity, since we only know ourselves through our perceptions. That is, the “I” is always changing.
The Concept of God
Hume denies that God can be considered the cause of the world, as this notion lacks empirical support. We have no impression of divinity, and since knowledge is limited to impressions, we can assert that the idea of God does not belong to the scope of reason. Mechanistic thinking is not acceptable.
The External World
Seeing that we do not know the origin of our impressions, we cannot affirm the existence of a progression in our external world. This view is called “phenomenalism,” meaning that the limits of reality are our perceptions (to be is to be perceived). This leads to skepticism.