Cornerstones are the basis of a framework for developing one’s Leadership skills and capabilities. In this framework, these four Cornerstones are the primary, fundamental characteristics for leaders today.
Might there be other Cornerstones? Yes.
For example if you are a leader in a religious or spiritual community, then, Spirituality might be fundamental for you. Or if you work in the world of not-for-profit foundations, then Service might be a fundamental.
The key here is that each Cornerstone is a core characteristic for your leadership development and application.