Full Idea
Scientism says that the exact sciences are the leading sources of knowledge about the world.
Gist of Idea
Scientism says most knowledge comes from the exact sciences
Source
Robert Hanna (Rationality and Logic [2006], 1.2)
Book Reference
Hanna,Robert: 'Rationality and Logic' [MIT 2006], p.9
A Reaction
I almost agree, but I would describe the exact sciences as the chief 'evidence' for our knowledge, with the chief 'source' being our own ability to make coherent sense of the evidence. Exact sciences rest on mathematics.