Descartes & Locke: A Philosophical Discourse on Knowledge & Existence
Descartes: Doubt and the Criterion of Truth
Methodical Doubt
Doubt, for Descartes, is a method for reaching indubitable truth. It applies universally and involves three phases:
- Doubting the Senses: Senses often deceive us, making them unreliable.
- Doubting Immediate Experience: The dream hypothesis questions the reality of our perceptions.
- Doubting Mathematics: Even mathematical principles can be doubted.
The Undoubtable Truth
The only certainty is the act of doubting itself (“I think, therefore I am”). This leads to a focus on the thinking subject (nativism), suggesting some knowledge is innate.
Types of Ideas
- Adventitious Ideas: Derived from sensory experience (e.g., the color of the sun).
- Factitious Ideas: Constructed by the mind from other ideas (products of imagination).
- Innate Ideas: Present in the mind from birth; fundamental, clear, and distinct, grasped through intuition.
Clear ideas are those without doubt. Distinct ideas are separate and unconfused with others.
The Three Substances
God as Guarantor
Demonstrating God’s Existence
Descartes argues for God’s existence to address the possibility of an evil genius deceiving us. He offers two proofs:
- The Argument from Innate Ideas: The idea of a perfect and infinite God cannot be adventitious or factitious, therefore it must be innate, placed in our minds by God.
- The Ontological Argument: A perfect being must exist, as existence is a perfection.
God, being good, would not deceive us about the existence of the world.
The Existence of the World
If God exists, so does the world, composed of extended bodies in motion. Primary qualities (innate ideas) like size, shape, and motion are distinct from secondary qualities (adventitious) like color and taste. The world is essentially a mathematical realm governed by fixed physical laws.
Dualism
Humans are composed of two substances: body (extended and mechanical) and soul (thinking). These are distinct and independent. The body is perceived through senses (subject to doubt), while the soul is perceived through reason (without doubt). The pineal gland is the point of interaction between body and soul.
Locke’s Critique of Innateness
Locke challenges the rationalist notion of innate ideas, arguing that universal consensus does not prove innateness, as children and those with cognitive impairments do not possess these ideas. He suggests that apparent universal agreement can arise from shared sensory experiences.
Locke’s Empiricist Thesis
Locke posits that all knowledge comes from sensory experience. The mind is a tabula rasa (blank slate) at birth. Experience is twofold:
- Sensation: Experience of external things (e.g., bitter, red, sweet).
- Reflection: Inner experience of the mind’s operations (e.g., love).
Locke believes in the principle of causality and that our ideas are the effects of an external world.