Full Idea
You sometimes speak of gravity as essential and inherent in matter. Pray do no ascribe that notion to me; for the cause of gravity is what I do not pretend to know.
Gist of Idea
I do not pretend to know the cause of gravity
Source
Isaac Newton (Letters to Bentley [1692], 1693.01.17)
Book Reference
Newton,Isaac: 'Philosophical Writings' [CUP 2004], p.100
A Reaction
I take science to be a two-stage operation - first we discern the regularities, and then we explain them. Evolution was spotted, then explained by Darwin. Cancer from cigarettes was spotted, but hasn't been explained. Regularity is the beginning.