0 the most important reason for something; the thing that makes something else happen:
Work was the mainspring of his life.
Most analysts begin, of course, with fundamental prejudices about the mainsprings of action in the social world.
The dream's mainspring is not a wish, but a gaze into the past.
Yet its avoidance is one of the mainsprings of behavior.
Laudianism, by contrast, emerges in this article as politically potent, and its ideological mainsprings invite further research.
All three mainsprings, then - interest, morality, and honor - coincided and complemented one another.
Nevertheless, we cannot dismiss its role as the plot's mainspring.
Fertile land is the mainspring upon which all stock grows.
I think that here the mainspring can be one of two beings.