Who Said That?

I've begun again my academic readings; currently I am in E. D. Hirsche's Validity in Interpretation, a 1967 book I have often wanted to read when time permitted. This book addresses a tremendous issue that is vitally important to my life and to yours whether you know it or not.

Who decides what the Bible means?
Who decides what the U.S. Constitution means?
Who decides what my insurance policy means?

In all three cases, what if someone with more clout disagrees with my interpretation? Whose interpretation is valid?

Here's the beginning of an answer:
Whenever meaning is attached to a sequence of words it is impossible to escape an author.

When you want to know what a statement means, you should find out who said it. You can't get inside his/her head, but this all-important bit of knowledge is the starting point for communication.

Thus, when critics deliberately banished the author, they themselves usurped his place, and this led unerringly to some of our present-day theoretical confusions. Where before there had been but one author, there now arose a multiplicity of them, each carrying as much authority as the next. To banish the original author as the determiner of meaning was to reject the only compelling normative principle that could lend validity to an interpretation.

In other words, if the original author does not determine what the the Constitution or the Bible means, then anyone can make it say what he/she wishes, with no "compelling normative principle" to rein in him/her.