Words for Reasoning and Frameworks
Some words that relate to systems of thought.

This particular twisty Word Journey started with me wondering if I was using "theory" correctly. (Ans: I was not.)
Ideas & Explanations
Theories are suggested ways to connect the parts, relationships, and principles of an entire system. Theories are at least partially verified, but not so much so that they'd be considered an official law.
A hypothesis is a proposed explanation that's a starting point for further investigation. A hypothesis is based on limited evidence; a theory is based on a lot more.
A conjecture is a guess -- perhaps an informed one, perhaps not -- but it doesn't require any proof, verification, or evidence at all.
Generally, when people say they have a "theory" or "hypothesis" they almost always mean they have a "conjecture."
Practical Tools
A standard is a model/measurement, of quantity or quality, that's established by authority, custom, or general consent.
Rubrics are clear rules or guidelines used to judge or evaluate something.
A heuristic is an informal, loosely defined rule -- especially an easily remembered and executed bit of guidance that helps someone find an answer that's good enough.
Foundational Truths
A principle is a fundamental truth from which other truths flow; principles direct, guide, or suggest behavior.
A maxim is a principle that is concisely stated or expressed.
Axioms are things that are self-evident or widely accepted as true without proof, which are then used as building blocks for additional reasoning.
Big Systems
A philosophy is the general set of laws, attitudes, or principles that guides behaviors, actions, and understandings.
A methodology is a system of methods and principles used when doing something.