It's a basic principle of statutory interpretation that legislatures define laws by their written text.
LMFTY: It's one basic principle in English Jurisprudence, known in legal circles as "the plain meaning rule". The other two are: "the golden rule" and "the mischief rule".
The golden rule allows a judge to depart from a word's normal meaning in order to avoid an absurd result.
The mischief rule sets the court to determine the "mischief and defect" that the statute in question has set out to remedy, and what ruling would effectively implement this remedy.
When America was founded those three principles were firmly in place. Over the years the courts and the laws themselves have been moving away from that tradition, creating the (in)famous loopholes that are the bread and butter of corporate law practice.