Naturalism is "the idea or belief that nothing exists beyond the natural world". It is the belief that "the natural world is the whole of reality". The term was first used this way in English in 1750.
Methodological or scientific naturalism is concerned with practical methods for acquiring knowledge.
Explanations for observations are only useful when they are based on hypotheses of natural causes. An explanation that relies on a natural mechanism that works according to certain rules is usable. Explanations that need miracles to work are not.
Methodological naturalism is the principle underlying all of modern science. Some philosophers extend this idea, so that it applies to all of philosophy as well. Science and philosophy, according to this view, are said to form a continuum. W.V. Quine, George Santayana, and other philosophers have advocated this view.
A number of other philosophical ideas are similar to naturalism: