I often say the following, especially to philosophers.
Philosophy is the study of problems which cannot be solved.
As soon as a problem can be solved, it moves to the science faculty.
But one philosopher told me that at least in ethics, philosophers (i.e. philosophers in the academic/university system) do solve problems. Well, I can't agree with that. Ethics is the study of what should be. Science is the study of what is. So ethics can never be a science. One can, however, systematize ethics in terms of an axiomatic system or various rule-based systems. But just because something looks very technical doesn't mean it's a science. (Take astrology for example!)
Historically, many subjects were actually a part of religion, not philosophy. As more has become known about geology, biology, medicine, cosmology and psychology, these subjects have moved to the science faculty. People used to give gifts to the god Asclepius to cure diseases, and they gave gifts to the gods of harvests to get a successful crop. Now people give their gifts to doctors and seed and fertilizer companies.
So to answer the question, some subjects never acquired objective means of obtaining knowledge.
I think also that many areas of philosophy are actually conducted within each field, like philosophy of mathematics, philosophy of physics, and so forth. It's a bit like mathematics because mathematics is a tool which is applied to dozens of subjects. Philosophy can also be regarded as a method, which can be applied to any subject. So every subject has its own philosophy now. The philosophy department of a university focuses mainly on applications of philosophical thinking to problems that are either not related to the real world, or are just not amenable to objective methods yet, like: "What is the nature of consciousness and awareness?"