An issue which is both highly personal and quite universal is the problem of the nature of man or the mind-body problem. Is man different from animals, plants and machines? Will robots or computers ever be identical to man? Those who hold the view that people are nothing but physical matter adhere to materialism. Those who argue that man has both a physical body and a mind which exists apart from the physical brain are proponents of the dualism theory. If man is not totally a physical being, then what happens to his mind (or soul) when the body dies? Controversial issues of spirituality and immortality are raised immediately with this line of thought.Assuming that man does possess both a body and a mind, how do the two relate to one another? Interactionism holds that both the mind and the body can causally affect each other. Epiphenomenalism, on the other hand, states that physical events can cause mental events, but occurrences in the mind are not able to cause physical events. A third theory is that only the mind exists and that the material world, including the body, are simply perceptions in the mind. This brings up a fundamental question: How do you know that there are any minds at all besides your own?A sixth major area of philosophical inquiry is knowledge and science. How do we know anything? A fundamental issue is whether knowledge can be derived from pure reason or whether knowledge must be based on sense experiences. Rationalism holds with the former. Empiricism holds with the latter. The empiricist further distinguishes two kinds of science. These are formal or conceptual sciences, like logic and mathematics, and objective sciences, like physics and psychology.An almost frightening result of such inquiries is the realization that in fact there may or may not be an external world at all. This type of skepticism leaves one stuck with nothing you can be sure of! Whether absolute certainty about anything can be obtained is an inevitable controversy which arises when one attempts to wrestle with this problem.