In the philosophy of science, there are several definitions of protoscience. Its simplest meaning (most closely reflecting its roots of + science) involves the earliest eras of the history of science, when the scientific method was . Thus, in the late 17th century and early 18th century, Isaac Newton contributed to the dawning sciences of chemistry and physics even though he was also an alchemist who sought chrysopoeia in various ways, some of which were unscientific. Our era views his as one of protoscience. Another meaning extends this idea into the present, involving the distinction between hard and soft sciences, in which various sciences (or branches thereof) are ranked according to methodological rigor. In this sense, the physical sciences may be posited as science whereas psychoanalysis may be labeled as protoscience because not all of its theoretical basis is empirical. Protoscience in this sense is sometimes distinguished from pseudoscience by a genuine willingness to be changed through new evidence, as opposed to having theory that can always find a way to rationalize a predetermined belief. Compare fringe science, which is considered highly speculative or even strongly refuted. Some protosciences go on to become an accepted part of mainstream science.