Natural philosophy is a term applied to the objective study of nature and the physical universe before the development of modern science.
In other words, all forms of science historically developed out of philosophy or more specifically natural philosophy. At older universities, long-established Chairs of Natural Philosophy are nowadays occupied mainly by professors of physics.
Natural philosophy was the term whose usage preceded our current term science in the sense that prior to the replacement of the term "natural philosophy" with the term science, the term science was used exclusively (and comparatively rarely) as a synonym for knowledge or study and when the subject of that knowledge or study was 'the workings of nature', then the term "natural philosophy" would be used.
Robert Boyle wrote what is considered to be a seminal work on the distinction between nature and metaphysics called A Free Enquiry into the Vulgarly Received Notion of Nature . This book, written in 1686, marked the point where the scene was set for natural philosophy to turn into science.
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