Full Idea
Nothing's outside your scope when it comes to measurement. Well, if you're such an expert, measure a man's soul; tell me how large or how small that is.
Gist of Idea
If everything can be measured, try measuring the size of a man's soul
Source
Seneca the Younger (Letters from a Stoic [c.60], 088)
Book Reference
Seneca: 'Letters from a Stoic (Selections)', ed/tr. Campbell,Robin [Penguin 1969], p.154
A Reaction
This is Descartes's non-spatial argument, which I take to be one of the four main props to his mind-body dualism. As always, it is expressed with beautiful concision by Seneca.