Aristotle's views of reality were enshrined in what he referred to as his "first philosophy," or what we today call metaphysics. This involved in-depth study of the universal principles and qualities of all material existence. He had studied biological and other scientific phenomenon while employed as a teacher and came to believe that the natural world as we know it was real, physical and tangible. He believed we could use our senses of sight, sound, smell, taste and touch to identify Earth's natural forms. If one could identify something's form, one could explain both what and why it is.
This was a vast departure from the teachings of his mentor, Plato, who, in his book The Republic, used his "Allegory of the Cave" to essentially state that everything we perceive in this world is an illusion—just shadows dancing on a wall, an artificial replica of the real thing, which exists in perfect form in some other world. Aristotle's view that reality is definable and identifiable and tangible as we experience it eschewed Plato's notions of reality as abstract and grounded it in root causes. In other words, if we could explain how and why something was, what it's purpose and uses were, then we could explain what it was.