In his Profound Knowledge, Dr. Deming introduced Systems Thinking. He defined a system as a set of interrelated parts aligned for a common aim. See Dr. W. Edwards Deming and Profound Knowledge – Part 1.
Variation was another aspect of Profound Knowledge: variation exists in all things and if we study it properly, we know what actions to take. See Dr. W. Edwards Deming and Profound Knowledge – Part 2.
His Theory of Knowledge reinforced scientific thinking: there is no knowledge without theory. See Dr. Deming and Profound Knowledge – Part 3.
The fourth cornerstone, Knowledge of Psychology, had mostly to do with human motivation: people are intrinsically motivated and rewards/punishment have little to do with improving performance. People also love learning and experiencing joy/pride in work. For further study, refer to Dr. W. Edwards Deming and Profound Knowledge – Part 4.
They are all intertwined in a new philosophy of leadership.