Philosophy was long regarded as the sole method of thought that would explain phenomena, be it imaginary, concrete, celestial, or terrestrial. Aristotle was a biologist, if we look at his work from today's perspective. He was mainly interested in the species that scattered all over the places. His concern was to collect as many different animals and plants as possible, so that he would have been able to talk about them with greater certainty. However, he was also a strong advocate of categorization and in order to categorize what he had collected, he needed to contemplate on what to put in this or that category or on what makes two things different. This contemplation made him a philosopher, as we understand it today.
You can't grasp the truth in your hand, you may only touch it.