Naturalism is a school of thought about the nature of reality (that excludes any elements of the super natural).
Naturalism… is a comprehensive worldview based in a scientific, empirical understanding of reality.
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Naturalism, in essence, is simply the idea that human beings are completely included in the natural world: there’s nothing supernatural about us. Naturalism is based on science as the best, most reliable means for discovering what exists. Science shows that each and every aspect of a human being comes from and is completely connected to the natural world, and is understandable in terms of those connections.
Please visit naturalism.org to explores the naturalism school of thought. They also have a free PDF book that summarizes naturalism very well. I highly encourage you to download and study it at your leisure.