What is the best meaning of the term “the irreducible plurality of values”?

The best meaning of the term is that there are some values, such as the value of human life or certain aesthetic goods, cannot be condensed to measurable utility. This results from such values being equally right and significant but incongruent which each other

according to worldatlas.com, the u.s. has an 86% literacy rate.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.