Final answer:
The principle of government expressed by the statement 'The purse and sword must not be in the same hands' is separation of powers.
Step-by-step explanation:
The principle of government expressed by the statement 'The purse and sword must not be in the same hands' is separation of powers. This principle is a fundamental aspect of the Constitution's design.
It involves the division of government into three separate branches which are responsible for different functions: legislative, executive, and judicial.