Definition:
Naturalism is the philosophical doctrine that everything that exists belongs to the natural world and can be understood through natural causes and laws. It rejects supernatural explanations and maintains that reality can be investigated through science, observation, and reason. In ethics, naturalism often attempts to ground moral values in human nature and empirical facts.

Thinkers:

• John Dewey
• Willard Van Orman Quine
• Aristotle

Example:
Explaining human emotions through biological and psychological processes reflects naturalism.