  Metaphysics, then, studies the ways in which anything that is can be said or thought to be. Leaving to sciences like biology or physics or mathematics or psychology the task of addressing the special ways in which physical things, or living things, or mathematical objects, e.g., numbers, or souls (minds) come to have the peculiar qualities each, respectively, has, the subject-matter of metaphysics are principles common to everything. Perhaps the most general principle is: to be is to be something. Nothing just exists, we might say. This notion implies that each entity/item/thing has at least some one feature or quality or property. Keeping at a general level, we can provisionally distinguish three factors involved when anything is whatever it is: there is that which bears or has the property, often called the ‘subject’, e.g., Socrates, the number three, or my soul; there is the property which is possessed; e.g., being thin, being odd, and being immortal; and there is the manner or way in which the property is tied or connected to the subject. For instance, while Socrates may be accidentally thin, since he can change, that is, gain and lose weight, three cannot fail to be odd nor, if Plato is correct, can the soul fail to be immortal. The metaphysician, then, considers physical or material things as well as immaterial items such as souls, god and numbers in order to study notions like property, subject, change, being essentially or accidentally.