Philosophy is the discipline concerned with the questions of how one should live (ethics); what sorts of things exist and what are their essential natures (metaphysics); what counts as genuine knowledge (epistemology); and what are the correct principles of reasoning (logic).

The word itself is of Greek origin: φιλοσοφία (philosophía) is a compound of φίλος (phílos: friend, or lover) and σοφία (sophía: wisdom).

Though no definition of philosophy is uncontroversial, and the field has historically expanded and changed depending upon what kinds of questions were interesting or relevant in a given era, it is generally agreed that philosophy is a method, rather than a set of claims, propositions, or theories. Some think that philosophy examines the process of inquiry itself; others, that there are essentially philosophical propositions which it is the task of philosophy to prove.

Although the word "philosophy" originates in the Western tradition, many figures in the history of other cultures have addressed similar topics in similar ways. The philosophers of the Far East are discussed in Eastern philosophy, while the philosophers of North Africa and the Near East, because of their strong interactions with Europe, are usually considered part of Western Philosophy.

Western philosophy

Main branches of philosophy

To give an exhaustive list of the main divisions of philosophy is difficult, because various topics have been studied by philosophers at various times. Ethics, metaphysics, epistemology, and logic are usually included. Other topics include politics, aesthetics, and religion. In addition, most academic subjects have a philosophy, for example the philosophy of science, the philosophy of mathematics, and the philosophy of history.

Metaphysics was first studied systematically by Aristotle, though he did not use that term. He calls it "first philosophy"(or sometimes just "wisdom"), and says it is the subject that deals with "first causes and the principles of things". The modern meaning of the term is any inquiry dealing with the ultimate nature of what exists. Within metaphysics, ontology is the inquiry into the meaning of existence itself, sometimes seeking to specify what general types of things exist (though sometimes the term is taken to be equivalent to metaphysics). The philosophy of mind is a part of metaphysics.

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: the idea that all our beliefs and thoughts may be somehow illusory or mistaken.

Ethics, or 'moral philosophy', is concerned with questions of how agents ought to act. Plato's early dialogues constitute a search for definitions of virtue. Metaethics is the study of whether ethical value judgments can be objective at all.

Logic has two broad divisions: mathematical logic (formal symbolic logic) and what is now called philosophical logic, the logic of language.

Definitions of philosophy

What should, and what should not, be counted as philosophy – and who counts as a philosopher – has been heavily debated in the Western tradition. Historically, philosophy has been associated with certain broad topics, as outlined above. Still, the search continues for a pattern that unites the disparate philosophical activities and interests of those who study those subjects. A handful of candidate explanations can nevertheless be assembled. Several philosophers or philosophical directions have had opinions about what philosophy should be and should not be.

The very open-ended nature of philosophy makes many people skeptical when it comes to limiting the concept of philosophy to something more confined. Accordingly, metaphilosophical relativists may claim that any statement can be counted as a philosophical statement, as there is no objective way to disqualify it.

Some theorists adopt the stance that any given philosophy is merely a reflection of the way that a person is socially embedded in a certain culture. To put it in Hegel's terms, "philosophy is that which grasps its own era in thought."

Plato, or at least the protagonist in his dialogues, Socrates, held up a number of virtues proper to philosophers. One such virtue was the feeling of wonder at the world. Among other things, Plato rejected the idea that rhetoric had any place in philosophy (most famously in Gorgias). Along similar lines, George Berkeley claimed that philosophy was nothing other than the study of wisdom and truth. And still other virtues can be culled from the literature.

Many critics of philosophy have tried to deflate what goes on in one or another part of philosophy. The logical positivists denied the soundness of metaphysics, and therefore of most traditional philosophy. They affirmed that statements about metaphysics, religion, and ethics are devoid of cognitive meaning, and therefore nothing but the expression of feelings or desires. Another example is Nietzsche, who argued that philosophers "are not honest enough in their work, although they make a lot of virtuous noise when the problem of truthfulness is touched even remotely. They all pose as if they had discovered and reached their real opinions through the self-development of a cold, pure, divinely unconcerned dialectic[...]; while at bottom it is an assumption, a hunch, indeed a kind of 'inspiration' – most often a desire of the heart that has been filtered and made abstract – that they defend with reasons they have sought after the fact". Others, like Francis Bacon, have argued that philosophy contributes nothing, but is merely an echo of nature.

Still, positive conceptions of philosophy are not hard to find. What constitutes sound philosophical work is sometimes summed up by the term "philosophical method". Some philosophers have explained that philosophy is the pursuit and demarcation of the limits and powers of human reasoning. Also, it is often agreed that arguments should try to follow the rules of logic and avoid fallacies.

Many contemporary philosophers have argued that the scientific method should be followed as closely as the subject-matter allows. It is a commonplace view that once a branch of philosophy fully starts following the norms of science (i.e., use of the scientific method), it is no longer properly within the domain of "philosophy", but becomes a part of "science". Other views emphasize that philosophy is continuous with all areas of intellectual inquiry, including science.

Disparaging terms have been coined in order to provide examples of non-philosophers and non-philosophy. "Pseudophilosophy" is used to describe those activities that are not associated with a legitimate kind of inquiry, and "philosophaster" is a term used to describe those who engage in pseudophilosophy.