  We discuss the role of propositions, truth, context and observers in
scientific theories. We introduce the concept of generalized proposition and
use it to define an algorithm for the classification of any scientific theory.
The algorithm assigns a number 0, 1, 2 or 3 to a given theory, thereby
classifying it as of metaphysical, mathematical, classical or quantum class.
The objective is to provide an impartial method of assessing the scientific
status of any theory.
