Full Idea
We know the truth not only through our reason but also through our heart. It is through that latter that we know first principles, and reason, which has nothing to do with it, tries in vain to refute them.
Gist of Idea
The first principles of truth are not rational, but are known by the heart
Source
Blaise Pascal (Pensées [1662], 110 p.58), quoted by Terry Pinkard - German Philosophy 1760-1860 04 n4
Book Reference
Pinkard,Terry: 'German Philosophy 1760-1860' [CUP 2002], p.91
A Reaction
This resembles the rationalist defence of fundamental a priori principles, needed as a foundation for knowledge. But the a priori insights are not a feature of the 'natural light' of reason, and are presumably inexplicable (of the 'heart').