Full Idea
I do not recognise what the proportion of magnitude is between two and three, unless I consider a third term, namely unity, which is the common measure of the one and the other.
Gist of Idea
I can only see the proportion of two to three if there is a common measure - their unity
Source
René Descartes (Rules for the Direction of the Mind [1628], 14)
A Reaction
A striking defence of the concept of the need for the unit in arithmetic. To say 'three is half as big again', you must be discussing the same size of 'half' in each instance.
Book Reference
Descartes,René: 'Rules for the Direction of the Mind' [Newcomb Library 2023], p.56