Aristotle defined nature “as an internal origin of change or stability”1. Natural substances are things like animals, plants, and inanimate matter like earth, water, fire, and air. Every natural substance according to Aristotle has its own nature, which gives rise to its natural behavior/characteristic. The nature of a natural substance is its inner principle/source of change.2Therefore, natural substances are capable of moving, that is, growing, acquiring qualities, losing them and finally to be born and to die. In Book II of Physics and Parts of Animals, Book 1, Aristotle contrasts natural substances with artifacts. He states that these are also capable of movement, but they move based on what they are made of. He gives us an example of movement. wooden bed “if the bed grew, it would not be a bed but wood that would emerge”3. Here, Aristotle opposes two parts of nature: matter and form. An investigation into the matter principle leads him to establish an important distinction between form and matter. In this essay, I will explain and critically discuss why Aristotle argues that “we should talk about the form of a thing and the kind of character it also has.” , since the nature corresponding to the form is more important than the material nature”4. In Parts of Animals bk1, Aristotle begins his discussion of how we should investigate animals. He states that there are too many attributes common to species and that we should refine this and discuss which ones are distinguished by a difference in shape. He gives us an example of locomotion “it is obvious that locomotion is not a form because flying, swimming, walking and crawling are different”5. He also states that form is not simply like the early philosophers...... middle of article...... the scientist should first grasp the event and only then attempt to discover it the causes. Works Cited Barnes, Jonathan (ed.) The Cambridge Companion to Aristotle, (Cambridge University Press, 1995). Bodnar, Istvan, "Aristotle's Natural Philosophy", The Stanford Encyclopedia of Philosophy (Spring 2010 edition), Edward N. Zalta (ed.), URL=.Broadie, Sarah, PY2003 Conference, Weeks 5 and 6, Conference Paper (St Andrews 2011). Fine, Gail & Irwin, Terence (Translation), Introductory Readings in Aristotle, (Hackett Publishing Company 1996). Lennox, James, (Trans), Aristotle, On the Parts of Animals I to IV, (Oxford University Press 2001). The Stanford Encyclopedia of Philosophy (summer 2010 edition), Edward N. Zalta (ed.), URL http://plato.stanford.edu/entries/ aristotle-biology/