1. fundamental principles or basic elements of a subject
Usage: formal; often used in academic contexts
2. a work containing the basic principles of a science or art
Usage: often capitalized when referring to specific works

Examples

• The professor explained the principia of quantum mechanics to the graduate students.
• Newton’s Principia revolutionized our understanding of physics and mathematics.
• Students must master the principia before advancing to more complex theories.
• The textbook covers the principia of organic chemistry in its first three chapters.
• Her research focused on the principia underlying modern economic theory.
• The ancient Greek principia of geometry still influence mathematical education today.