first principles 
plural noun
The fundamental concepts or assumptions on which a theory, system, or method is based: I think we have to start again and go right back to first principles...
- The purpose of Rawl's work was to create a system of justice from first principles, creating a philosophical basis for a just society.
- I suspect that the universe is deterministic and based upon a set of first principles that are probably not comprehensible to any sort of being that is bound to causality.
- Incorporating these features enables the method to more effectively identify first principles.