descartes rational intuition and deduction

clear and distinct ideas

when a perception is present and accessible to the attentive mind and it is so sharply separated from all other perceptions

rational intuition

the ability to discover the truth of a claim just by thinking about it using reason

deduction

in a valid deductive argument, we use the premises which we know are true to reason a conclusion which therefore has to be true

Descartes’ rational intuition and deduction method

use rational intuition to recognise clear and distinct ideas and then build up knowledge via deductive arguments using clear and distinct ideas as the premises

descartes’ approach

1. doubt as much as possible (3 waves of doubt)

2. determine if we still know anything (the cogito)

3. identify what is special about this knowledge (clear and distinctness)

4. use this knowledge in deductive arguments to gain even more knowledge (about God and the external world)

causal adequacy

the cause of something must contain at least as much reality as its effect

A cannot cause B if A is less real than B

descartes’ cosmo arguement

p1. i exist as a being from one moment to the next

p2.i cannot be the cause of myself as i would have made myself perfect and i know i am not

p3. even if i had always existed, the fact that i continue to exist from one moment to the next would still require a cause

p4. i cannot be the cause of my continued existence because if i has the power to do this i would know that i had such power, but i do not

p5. no other finite being (my parents) could be the ultimate cause of my continued existence as my parents do not keep me in existence from moment to moment

c1. therefore, the only possible cause of my continued existence is a supremely prefect being (i.e. God)

c2. therefore God exists

descartes’ arguments for God

1. trademark argument

2. cosmological argument

3. ontological argument

Descartes’ reasoning for talking about God

Descartes’ needs to prove that a perfect God exists who would not allow him to be deceived in this way

Descartes’ trademark argument

P1. i have the concept of God

P2. my concept of God is the concept of something infinite and perfect

P3. but i am a finite and imperfect being

P4. the cause of an effect must have at least as much reality as the effect

C1. the concept of God has more reality than my mind

P5. the cause of my concept of God must have as much reality as what the concept is about

P6. so the cause of my idea of God must be an infinite and perfect being

C2. so God exists

Descartes’ ontological argument

1. we have an idea of God as a supremely perfect being

2. a supremely perfect being has all the perfections

3. existence is a perfection

4. therefore, a supremely perfect being, God, exists

development of the onto argument

the essence of God includes omnibenevolence, omnipotence and existence

Descartes believes that you cannot separate existence from God no more than you can separate the idea of a mountain from that of a valley/

arguments for phsycial substances and objects

Descartes has proved that his a priori knowledge is trust worthy using arguments from God and now he wants to prove that his a posterori knowledge is trsutworthy

Descartes’ argument for the possibility of physical objects

P1. i have a clear and distinct idea of what an object is

P2. if an idea is clear and distinct then it is not contradictory

P3. God exists and is a perfect being

P4. God can only make something that is non-contradictory

C1. therefore, God can make physical objects

C2. therefore, it is possible that physical objects exist

Descartes argument for the existence of physical objects

P1. i have perceptions of an external world with physical objects

P2. my perceptions must be cause by my own mind, God or physical objects

P3. my perceptions cannot be caused by my own mind because they are involuntary

P4. so, the cause of my perceptions must be something external to my mind

P5. following premise 2, the cause of my perception must be God or physical objects

P6. God exists

P7. if the cause of my perceptions is God and not the physical objects themselves, then God has created me with a tendency to form false beliefs from my perceptions (because i have perceptions of an external world)

P8. but God is a perfect being and would not create me with a tendency to form false beliefs

P9. so, i can trust my perceptions

C. so given premises 1 and 7, i can know that an external world of physical objects exists