You Must Make Metaphysical Commitments
Everyone in practice must make metaphysical commitments, that is, he or she must commit to some position concerning the fundamental nature of the world.
Perhaps, one can adopt and maintain consistently a theoretical position of skepticism about our ability to know the nature of the world. Such skepticism may take many forms. One may maintain that we cannot demonstrate the truth of beliefs about the world around us, much less beliefs about metaphysical entities such as God (e.g., Hume). Alternatively, one may hold that complete objectivity is not possible and hence there can be no such thing as objective knowledge in any discipline (e.g., Nietzsche).
Whether one can maintain a theoretical position of skepticism against all rebuttals is a question for the philosophers. However, it is clear that in practice one cannot. Practice is action. We have an inescapable decision to make--live or die. If we choose to live, we must act. We must do something. We must eat, sleep, work, play, get along with our neighbors, and act in myriad other ways. Living is acting. Now, to act is to translate thought into action. It is to make a decision. That decision--any decision--is based, explicitly or implicitly, on my beliefs about the nature of the world and my place in or relation to the world.
Commitment to a belief in the laws of nature
One such belief common to practically all of my decisions is that our world behaves in regular ways, which we call the laws of nature. These laws are based on the proposition that the future will be like the past in fundamental respects. Today's fundamental chemical, physical, and biological behaviors will be tomorrow's. Based on this belief, we prescribe and take drugs, build and cars, build and travel over bridges, buy and watch TV sets, cook by recipes, and on and on. Skeptics such as Hume and Santanyana have denied that we are justified in the proposition that the world exhibits uniform, regular behavior. We may debate the theory, but in practice we must act, decide, and believe, explicitly or implicitly, that the regularity of fundamental natural behaviors is a part of the fundamental or ultimate nature of our world.
The name we give to beliefs concerned with the ultimate nature of the world is metaphysics. From the foregoing, we see that in practice, we must have metaphysical beliefs, explicitly or implicitly. Because we decide and act on these beliefs, we are committed to them. Thus, in practice, we cannot be skeptics. In practice, we all must make metaphysical commitments.