René Descartes (Leaving Cert Religious Education): Revision Notes
René Descartes
Who was René Descartes?
René Descartes (1596-1650) was a French philosopher considered the founder of modern philosophy. He lived during a time of scepticism and conflicting knowledge claims, when there was no reliable method for establishing firm foundations of knowledge. Traditional authorities and historical opinions were being questioned, creating uncertainty about what could truly be known.
Descartes lived during the Scientific Revolution, a period when traditional mediaeval worldviews were being challenged by new discoveries in astronomy, physics, and mathematics. This intellectual upheaval created both opportunities and anxieties about what could be known with certainty.
The method of systematic doubt
Descartes developed a revolutionary approach called systematic doubt to find absolute certainty. This method involved:
- Doubting anything that could possibly be false or uncertain
- Rejecting all knowledge gained through the five senses (since they can deceive us)
- Questioning the existence of the external world (since we might be dreaming)
- Stripping away all assumptions to find an unshakeable foundation
This approach is also known as Rationalism - the belief that the mind, rather than the senses, provides the starting point for certain knowledge (similar to Plato's philosophy).
Descartes' systematic doubt was not scepticism for its own sake, but a methodical tool designed to eliminate all uncertain knowledge in order to find what remains absolutely certain. This was a radical departure from mediaeval approaches that relied on authority and tradition.
"Cogito ergo sum" - the foundation of certainty
Through his systematic doubt, Descartes reached one undeniable conclusion: even if he was doubting or thinking false thoughts, he was still thinking. This led to his famous statement:
"Cogito ergo sum" - "I think therefore I am"
This became his bedrock of certainty because:
- Even false thoughts are still thoughts
- To doubt, one must be thinking
- To think, one must exist as a thinking being
- Therefore, his existence as a conscious, thinking being was undeniable
Worked Example: The Logic of Cogito
Step 1: Apply systematic doubt "Maybe everything I believe is false, maybe I'm being deceived about everything..."
Step 2: Recognise the paradox "But wait - if I'm doubting, then I must be thinking"
Step 3: Draw the inevitable conclusion "And if I'm thinking, then I must exist as a thinking being"
Step 4: Reach certainty "Therefore, 'I think, therefore I am' - this cannot be doubted"
Proving God's existence
From this foundation, Descartes needed to move beyond just knowing himself. He examined his consciousness and found the idea of God - a perfect, infinite being. He argued this idea was the clearest and most distinct of all ideas because:
- It couldn't come from his senses
- It couldn't be invented by human imagination
- It was unique and perfect
- The idea of infinity couldn't come from finite beings
Therefore, Descartes concluded that God must have placed this idea in human minds, meaning God exists. Since God is perfect, benevolent, and trustworthy, He guarantees that our clear understanding of the external world is correct.
Cartesian Dualism
Descartes' philosophy led to Cartesian Dualism - the division of reality into two distinct types of substance:
Res Cogitans (Thinking Substance)
- The mind/soul/spirit
- Internal and free
- Non-physical
- The realm of thoughts, consciousness, and reasoning
Res Extensa (Extended Substance)
- The physical world of matter
- External and mechanical
- Governed by physical laws
- Everything that has extension in space
Descartes believed humans are thinking beings linked to physical bodies. He called this connection "the ghost in the machine" - the mind (ghost) operating within the physical body (machine). However, he never satisfactorily explained how these two completely different substances interact.
The "interaction problem" in Cartesian Dualism remains one of philosophy's most challenging questions: if mind and matter are completely different substances, how do mental states (like deciding to move) cause physical effects (like actual movement)? This problem continues to influence debates in philosophy of mind today.
The mechanical universe
Descartes' dualism created a foundation for viewing the physical world as entirely mechanical:
- Matter behaves according to predictable laws of motion and inertia
- Every movement is theoretically predictable and determined
- The external world can be understood through geometry and mathematics
- Scientific experimentation became essential for understanding this mechanical realm
This mechanical view saw nature as operating like clockwork, with God as the creator who set everything in motion but then remained separate from the day-to-day workings of the universe.
Impact on religion and science
Descartes' intentions
Descartes originally wanted to:
- Establish firm foundations for scientific knowledge
- Free science from theological interference
- Maintain God's central role in his philosophical system
- Prevent his method from leading to a godless worldview
Unintended consequences
However, Descartes' work had several ironic effects:
Separation of God from nature: By creating a purely mechanical universe, Descartes made it easier for God to disappear from scientific understanding. Nature was no longer seen as the "Book" that reveals God, but simply as mechanical processes.
Path to Deism: Descartes paved the way for Deism - the belief that God created the universe but now remains outside it, no longer intervening in the mechanical world.
Gateway to Atheism: Some Enlightenment thinkers took the next logical step, arguing that if God cannot be seen in the mechanical universe, perhaps God doesn't exist at all. The absence of divine intervention became evidence for the non-existence of God.
Scientific independence: Once scientists possessed the mechanical method for understanding nature, they no longer needed God to explain natural phenomena.
Legacy and paradox
The great paradox of Descartes' work was that while he used philosophy to secure God's place in understanding the world, his rational construction actually made it easier for God to disappear from people's worldview. Together with Newton's scientific methods, Descartes contributed to both the rise of Deism in the 18th century and later Atheism.
This demonstrates how attempts to prove religious truth through reason and science can sometimes have the opposite effect, leading to purely secular explanations of reality.
Key Points to Remember:
- Descartes used systematic doubt to find absolute certainty, concluding "I think therefore I am"
- He developed Cartesian Dualism, separating mind (res cogitans) from matter (res extensa)
- His mechanical view of the universe was intended to support both science and religion
- Ironically, his work paved the way for Deism and later Atheism by removing God from day-to-day natural processes
- Descartes shows how attempts to reconcile religion and science can have unintended consequences for both