The following branches are the main areas of study:

• Metaphysics investigates the nature of being and the world. Traditional branches are cosmology and ontology.
• Epistemology is concerned with the nature and scope of knowledge, and whether knowledge is possible. Among its central concerns has been the challenge posed by skepticism and the relationships between truth, belief, and justification.
• Ethics, or 'moral philosophy', is concerned with questions of how persons ought to act or if such questions are answerable. The main branches of ethics are meta-ethics, normative ethics, and applied ethics. Meta-ethics concerns the nature of ethical thought, comparison of various ethical systems, whether there are absolute ethical truths, and how such truths could be known. Ethics is also associated with the idea of morality. Plato's early dialogues include a search for definitions of virtue.
• Political philosophy is the study of government and the relationship of individuals and communities to the state. It includes questions about justice, the good, law, property, and the rights and obligations of the citizen.
• Aesthetics deals with beauty, art, enjoyment, sensory-emotional values, perception, and matters of taste and sentiment.
• Logic deals with patterns of thinking that lead from true premises to true conclusions, originally developed in Ancient Greece. Beginning in the late 19th century, mathematicians such as Frege focused on a mathematical treatment of logic, and today the subject of logic has two broad divisions: mathematical logic (formal symbolic logic) and what is now called philosophical logic.
• Philosophy of mind deals with the nature of the mind and its relationship to the body, and is typified by disputes between dualism and materialism. In recent years there has been increasing similarity between this branch of philosophy and cognitive science.
• Philosophy of language is the reasoned inquiry into the nature, origins, and usage of language.

Most academic subjects have a philosophy, for example the philosophy of science, the philosophy of mathematics, the philosophy of logic, the philosophy of law and the philosophy of history. In addition, a range of academic subjects has emerged to deal with areas which would have historically been the subject of philosophy. These include psychology, anthropology and science.

Notes:

1. Jenny Teichmann and Katherine C. Evans, Philosophy: A Beginner's Guide (Blackwell Publishing, 1999), p. 1: "Philosophy is a study of problems which are ultimate, abstract and very general. These problems are concerned with the nature of existence, knowledge, morality, reason and human purpose."
2. A.C. Grayling, Philosophy 1: A Guide through the Subject (Oxford University Press, 1998), p. 1: "The aim of philosophical inquiry is to gain insight into questions about knowledge, truth, reason, reality, meaning, mind, and value."
3. Anthony Quinton, in T. Honderich (ed.), The Oxford Companion to Philosophy (Oxford University Press, 1995), p. 666: "Philosophy is rationally critical thinking, of a more or less systematic kind about the general nature of the world (metaphysics or theory of existence), the justification of belief (epistemology or theory of knowledge), and the conduct of life (ethics or theory of value). Each of the three elements in this list has a non-philosophical counterpart, from which it is distinguished by its explicitly rational and critical way of proceeding and by its systematic nature. Everyone has some general conception of the nature of the world in which they live and of their place in it. Metaphysics replaces the unargued assumptions embodied in such a conception with a rational and organized body of beliefs about the world as a whole. Everyone has occasion to doubt and question beliefs, their own or those of others, with more or less success and without any theory of what they are doing. Epistemology seeks by argument to make explicit the rules of correct belief formation. Everyone governs their conduct by directing it to desired or valued ends. Ethics, or moral philosophy, in its most inclusive sense, seeks to articulate, in rationally systematic form, the rules or principles involved."
4. Philosophia, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
5. Online Etymology Dictionary
6. The definition of philosophy is: "1.orig., love of, or the search for, wisdom or knowledge 2.theory or logical analysis of the principles underlying conduct, thought, knowledge, and the nature of the universe". Webster's New World Dictionary (Second College ed.).