Naturalism is the belief that we can acquire knowledge of how the world works by studying natural phenomena, not supernatural causes. Everything in the universe, from the existence of life to the motions of the planets and interactions between objects, is said to be governed and ruled by natural laws that humanity can investigate and understand. Naturalism is a belief that only natural phenomena exist, both in existence and in how knowledge is obtained.
In Novum Organum Scientiarum (1620,) Francis Bacon wrote:
The subtlety of nature is greater many times over than the subtlety of the senses and understanding; so that all those specious meditations, speculations, and glosses in which men indulge are quite from the purpose, only there is no one by to observe it.
Questions about how the universe came to be, and why events happen as they do, are likely as old as humanity itself. Thinkers such as Thales of Miletus proposed naturalistic solutions to such fundamental questions as early as the sixth century BCE. During the Renaissance (c. 1450-1600), naturalistic explanations became more prominent.
In 1620, English philosopher Francis Bacon (1561-1626) published Novum Organum Scientiarum (New Instrument of Science), in which he proposed a method of learning called inductive reasoning, where conclusions are drawn from observed data, instead of implied from presumed principles. Inductive reasoning, and the investigative method on which it is based, became essential to scientific inquiry.
The natural world is, for the most part, one that is knowable, measurable, quantifiable, and predictable. Naturalism presumes that the world as we see it is what it is. In contrast, belief in supernatural phenomena stands in the way of understanding the world; humanity cannot exert control over supernatural phenomena or influence them, and, even worse, it can provide no explanation or reason for their actions.