Plato's Middle Period Metaphysics and Epistemology
a. Students of Plato and other ancient philosophers divide philosophy into three parts: Ethics, Epistemology and Metaphysics. While generally accurate and certainly useful for pedagogical purposes, no rigid boundary separates the parts. Ethics, for example, concerns how one ought to live and focuses on pleasure, virtue, and happiness. Since, according to Plato (and Socrates), virtue and happiness require knowledge, e.g., knowledge of goods and evils, Plato's ethics is inseparable from his epistemology. Epistemology is, broadly speaking, the study of what knowledge is and how one comes to have knowledge. Among the many topics included in epistemology are logic, belief, perception, language, science, and knowledge. (‘Science’ derives from the Latin ‘scientia’, which in turn translates the Greek ‘episteme’, from which English derives ‘epistemology’.) Integral to all of these notions is that they (typically) are directed at something. Words refer to something; perception (aesthesis in Greek) involves perceptibles; knowledge requires a known. In this respect, epistemology cannot be investigated without regard to what there is.
b. Metaphysics, or alternatively ontology, is that branch of philosophy whose special concern is to answer the question ‘What is there?’ These expressions derive from Aristotle, Plato's student. In a collection of his works, the most detailed treatise on the general topic of things that are comes after a treatise on natural things, ta phusika (from which English derives ‘physics’). Since the Greek for ‘after’ is meta, this treatise is titled ‘Metaphysics’. In that work one finds the famous formula that (first) philosophy studies being—the Greek for which is on—qua being. Hence the account of being is ‘ontology’—the English suffix ‘-ology’ signifying ‘study of’: e.g., biology is the study of living things.
c.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.