Sep 18-22 - Hobbes and Descartes’ Idea Idea

1. Hobbes

• The Idea Idea = the analysis-synthesis theory of deductive reasoning is a theory of how the mind works – by the algebraic decomposition and recombination of ideas. TTT p73-4

• Psychologism = the view that logic is a theory of how the mind works – but how can something about the functioning of the mind explain the necessity of deductive reasoning? (Can anything?) Platonic recollection? Aristotelian intuition?

2. Descartes

• We are endowed with mental faculties that guarantee the reliability of analysis and synthesis. (TTT p75)

• ‘Intuition’:

(a) of logically simple basic facts

(b) of logically simple deductive steps

• ‘Deduction’: intuition of simple steps + reliable memory of steps

• How can we tell whether we have employed these faculties correctly? When they are:

• ‘Clear’ = ‘present and manifest to an attentive mind’ – e.g., pain – and …

• … ‘distinct’ = ‘separate from other ideas’ – unlike, e.g., pain. E.g.,

• Nothing comes from nothing

• Something cannot both be and not be simultaneously

• What has been done cannot be undone

• Thinking entails existence

• The distinction between mental and material substances

• But even supposing (against all appearances) that this account helpfully identifies some mental faculties, what guarantees their reliability according to Descartes?

(1) Cogito ergo sum – intuition of my existence as a thinking thing

(2) I am certain of the contents of my own mind

(3) I have an idea of God – Anselm’s argument for the existence of the GCB

(4) A perfect being would not deceive by definition, so intuition is reliable

3. Leibniz

• The first attempt at an algebraic formulation of logic – of mechanical reasoning beyond just analysis and synthesis.