Full Idea
Our sentences cannot be divided into two classes, empirical and a priori, the truth of one to be decided by observation, the other by ratiocination. They lie on a scale, with observational sentences at one end, and mathematical ones at the other.
Gist of Idea
Empirical and a priori knowledge are not distinct, but are extremes of a sliding scale
Source
Michael Dummett (Thought and Reality [1997], 5)
Book Reference
Dummett,Michael: 'Thought and Reality (Gifford Lectures)' [OUP 2006], p.59
A Reaction
The modern post-Kantian dissolution of the rationalist-empiricist debate. I would say that mathematical sentences require no empirical evidence (for their operation, rather than foundation), but a bit of reasoning is involved in observation.