30 Philosophers, Chapter 24, Locke, Touchstone 62: Checks and Balances.

For the preservation of individual liberty and the prevention of tyranny, political power must be distributed among different branches of government—executive, legislative, and judicial. It is grounded in the idea that human nature is easily corruptible and concentrating power is dangerous. This diversification embodies the philosophical idea of checks and balances and ensures that no single authority goes unchecked.