Philosophy will not give you definite truths. When the definite truth about anything becomes possible, the subject moves out of the domain of philosophy and becomes a science. The aim of philosophy is limited to developing a systemic view of the knowledge that we derive from the sciences and analyzing the nature of our beliefs regarding morality, limitations of knowledge, and the nature of the universe and our place in it.
In the time of Plato and Aristotle, geometry, astronomy, and biology were included in philosophy. Mathematics was included in philosophy till the time of Newton—his book was called Philosophiæ Naturalis Principia Mathematica (The Mathematical Principles of Natural Philosophy). The study of atoms was in the domain of philosophy up to the end of the 19th century, and so was the study of mind and human psychology. Some subjects like Quantum Mechanics and the Darwinian Theory of Evolution are too nebulous to involve empirical testing and span across the domains of philosophy and science.
All subjects have a beginning in philosophy and they move into the domain of science when it becomes possible to find definite truths in them.