The principle ( or beginning) of anything is the most powerful part of a thing.

Explanation

(English-origin maxim.) The origin or foundation of a right, grant, or obligation controls its entire subsequent operation — challenge the root and the whole structure falls.

Where this applies

• A contract is challenged because the consideration was inadequate, and the court examines the original terms at the time of formation because the beginning of the agreement is its most powerful part.
• A corporation's charter is ambiguous, and the court resolves the ambiguity by looking at the original articles of incorporation rather than later amendments because the founding document controls.
• A constitutional provision is reinterpreted by a modern court, but the dissent argues that the original understanding at the time of ratification must govern because the principle of a thing is its most powerful element.