Is hermeneutics primarily descriptive or prescriptive?

Source: Webster's Revised Unabridged Dictionary (1913)

Hermeneutics \Her`me*neu"tics\, n. [Gr. ? (sc. ?).] The science of interpretation and explanation; exegesis; esp., that branch of theology which defines the laws whereby the meaning of the Scriptures is to be ascertained. --Schaff-Herzog Encyc.

If hermeneutics defines the scientific laws for obtaining meaning from scripture, then much of what is practiced is not hermeneutics but mere Greek rhetorical invention. After having studied the words, the grammar, the historical context, the personalities of the writers and his audience, and the culture of any possible influence upon the author, the interpreter then asks, "What do I think the author meant?" and scientific observation is supplanted by free-for-all invention. [1] The guess work is justified by all the observation which is countered by another interpreter's observations.

A scientific result is reproducible by others. The results of modern hermeneutics are not. [2] The various meaning derived (even using the same method) show that the methods are not valid (a technical term applied to a methodology).

In practice, the only science being conducted is in the observation of the methods used (which is your experience), and therefor it is descriptive. As a description of a method, an individual may adopt the method as an exegetical philosophy hoping to remain within the bounds of the described ideal.

The exception is with sensus plenior, which is independently reproducible due to the nature of the constraining rules.

[1] There is no objective standard by which one can measure sufficient study of "the words, the grammar, the historical context, the personalities of the writers and his audience, and the culture of any possible influence upon the author". The law of Universal ignorance declares that you cannot know what you do not know. Perhaps the author's unknown second cousin did something to the author in childhood that cannot be known, but influenced his intent. Piling facts upon the text does not ensure scientific objectivity. The final step is always subjective, and is therefor not scientific.

[2] If a standardized reproducible result cannot be produced, there can be no measure of 'good' or better' in the application of hermeneutic methods. The standard is simply 'Do I like it'. The one objective standard we have, that of the Apostles' methods, is rejected as strange and inventive.