Full Idea
The three key ideas that I have settled on in the history of ideas are: the soul, Europe, and the experiment.
Gist of Idea
The three key ideas are the soul, Europe, and the experiment
Source
Peter Watson (Ideas [2005], Intro)
Book Reference
Watson,Peter: 'Ideas: from fire to Freud' [Phoenix 2006], p.9
A Reaction
The soul is a nice choice (rather than God). 'Europe' seems rather vast and indeterminate to count as a key idea.