Full Idea
There are truths that instruct, perhaps, but they do not illuminate. In this class are all the truths of reasoning.
Gist of Idea
The truths of reason instruct, but they do not illuminate
Source
Joseph Joubert (Notebooks [1800], 1800)
Book Reference
Joubert,Joseph: 'Notebooks', ed/tr. Auster,Paul [nyrb 2005], p.60
A Reaction
A rather romantic view, which strikes me as false. An inspiring truth can suddenly collapse when you see why it must be false. Equally a line of reasoning can lead to a truth which need becomes an illumination.