Full Idea
The motions which the planets now have could not spring from any natural cause alone, but were impressed by an intelligent agent.
Gist of Idea
The motions of the planets could only derive from an intelligent agent
Source
Isaac Newton (Letters to Bentley [1692], 1692.12.10)
Book Reference
Newton,Isaac: 'Philosophical Writings' [CUP 2004], p.95
A Reaction
He is writing to a cleric, but seems to be quite sincere about this. Elsewhere he just says he doesn't know what causes gravity.