Reasoning from First Principles

Definition

A thought process that breaks down complex systems to their most basic, self-evident assumptions, and then building step-by-step from these granular pieces to a logical whole.

Origin

The concept as a philosophy stems from Aristotle and the notion of First Cause. This evolved into postulates by the Kantians, and later into postulates and axioms in mathematics. The "reasoning from first principles" concept was later popularized by Terence Irwin’s 1989 book “Aristotle’s First Principles.” (source)

Everyday Use

So often we do things simply because that's the way that they've been done, but we don't allow ourselves the time or opportunity to take a step back and evaluate if they're actually working, or how we can think about them differently. Reasoning from First Principles helps us to see the system from its component parts, and thus to gain new insights and a firmer understanding of the systems in our lives.