Suppose we seek to establish “Every human is an animal.” Understanding the meanings of “human,” “animal,” and “every” provides conceptual preliminaries. Relevant accepted premises or an appropriate argument supply propositional foundations. The proposition being established is the issue.
An established result in one discipline can become an accepted premise in another. The distinction survives because the roles are relative to the inquiry at hand.
Principles allow an investigation to proceed; its issues are the claims the science aims to settle.