Ancient Greek philosophy may be divided into the pre-Socratic period, the Socratic period, and the post-Aristotelian period. The pre-Socratic period was characterized by metaphysical speculation, often preserved in the form of grand, sweeping statements, such as "All is fire", or "All changes". Important pre-Socratic philosophers include Thales, Anaximander, Anaximenes, Democritus, Parmenides, and Heraclitus. The Socratic period is named in honor of the most recognizable figure in Western philosophy, Socrates, who, along with his pupil Plato, revolutionized philosophy through the use of the Socratic method, which developed the very general philosophical methods of definition, analysis, and synthesis. While Socrates wrote nothing himself, his influence as a "skeptic" survives through Plato's works. Plato's writings are often considered basic texts in philosophy as they defined the fundamental issues of philosophy for future generations. These issues and others were taken up by Aristotle, who studied at Plato's school, the Academy, and who often disagreed with what Plato had written. The post-Aristotelian period ushered in such philosophers as Euclid, Epicurus, Chrysippus, Hipparchia the Cynic, Pyrrho, and Sextus Empiricus.Medieval philosophy
The medieval period of philosophy came with the collapse of Roman civilization and the dawn of Christianity, Islam, and rabbinic Judaism. The medieval period brought Christian scholastic philosophy, with writers such as Augustine of Hippo, Boethius, Anselm, Robert Grosseteste, Albertus Magnus, Roger Bacon, Bonaventure, Thomas Aquinas, John Duns Scotus, William of Ockham, Nicholas of Cusa, and Francisco Suárez. A female Christian philosopher of the period was a student of Abelard named Heloïse. The philosophers in the scholastic Christian tradition and philosophers in the other major Abrahamic religions (such as the Jewish philosophers Saadia Gaon and Maimonides, and the Muslim philosophers Avicenna, Al-Ghazali, and Averroes) were each aware of the others' works. These religious traditions took on questions about the relation of man to God. The philosophy of this period is characterized by analysis of the nature and properties of God; the metaphysics involving substance, essences and accidents (that is, qualities that are respectively essential to substances possessing them or merely happening to be possessed by them), form, and divisibility; and logic and the philosophy of language.
Many of these philosophers took as their starting point the theories of Plato or Aristotle. Others, however, such as Tertullian, rejected Greek philosophy as antithetical to revelation and faith.Modern Western philosophy
Modern philosophy is generally considered to begin with the work of René Descartes. His work was greatly influenced by questioning from his correspondences with other philosophers. For example, the prodding of Pierre Gassendi and Princess Elizabeth of Bohemia obliged Descartes to try to formulate more cogent replies to the mind-body problem. 
Medieval philosophy had been concerned primarily with argument from authority, and the analysis of ancient texts using Aristotelian logic. The Renaissance saw an outpouring of new ideas that questioned authority. Roger Bacon (1214–1294?) was one of the first writers to advocate putting authority to the test of experiment and reason. Niccolò Machiavelli (1469–1527) challenged conventional ideas about morality. Francis Bacon (1561–1626) wrote in favor of the methods of science in philosophical discovery.Analytic and Continental
Main article: Analytic and Continental Philosophy
The late modern period in philosophy, beginning in the late 19th century and lasting to the 1950s, was marked by a developing schism between the "Continental" tradition and the "Analytic" tradition associated with many English-speaking countries.
What underlies the analytic tradition, especially the early analytic tradition, is the view (originally defended by Ockham) that much philosophical error arises from misunderstandings generated by language. According to some analytic philosophers, the true meaning of ordinary sentences is "concealed by their grammatical form", and we must translate them into their true form (understood as their logical form) in order to clarify them. The difficulty, so far unresolved, is to determine what the correct logical form must be. Some philosophers (beginning with Frege and Bertrand Russell) have argued that first-order logic shows us the true logical form of ordinary sentences. Other analytic philosophers, such as the late Wittgenstein, rejected the idea of logical form; and this issue of logical form figured prominently in early analytic philosophy. These debates over logical form are no longer as central to analytic philosophy as they used to be, and analytic philosophy now tends to address the full range of philosophical problems with all available philosophical methods. Today analytic philosophy's essence lies more in a style of writing and argumentation (that is, it aims to be clear and rigorous) than in its subject matter or ideas. An emphasis on carefully analyzing language to reveal philosophical errors still remains; but the “analysis” that figures in the name “analytic philosophy” is now just as likely to refer to the analysis of ideas, arguments, social institutions, and presuppositions.
"Continental" philosophy is most closely identified with the phenomenological movement inaugurated by Edmund Husserl and the various reactions to and modifications of Husserl's work. Phenomenology is primarily a method of investigation. As Husserl conceived it, to investigate phenomenologically is to examine the contents of conscious experience while bracketing all of the assumptions we ordinarily make concerning the existence of objects in the world. He believed that we could arrive at certain knowledge by deducing the necessary features of our conscious experience. Perhaps the most important such feature deduced by Husserl was called intentionality, which denotes the character of consciousness by which it is always directed at some object or other. The phenomenological method is an important alternative to the way that analytic philosophy typically proceeds. Instead of taking linguistic data as the starting point and linguistic analysis as the primary method of philosophy, phenomenology takes conscious experience as the starting point and the detailed analysis of such experience – that is, "phenomenological analysis" – as its method. Some important figures in the analytic tradition such as Wilfrid Sellars and Hector-Neri Castaneda have argued that linguistic analysis is actually a kind of phenomenological investigation because it appeals to our experience as language users to answer philosophical questions. In effect, they have argued that analytic philosophy is but one kind of phenomenology, the implication being that analytic philosophy can ignore the tradition that commences with phenomenology only to its detriment.
While Husserl placed great emphasis on consciousness and took up an idealist position motivated largely by a firm distinction between a conscious ego and its objects, the subject-object disinction was deeply critiqued by Husserl's student, Martin Heidegger. Heidegger's 1927 book Being and Time was not only a critique of Husserl, but of a way of thinking that he believed infected the entire Western philosophical tradition of which Husserl was the latest expression. Arguably, Being and Time was the single most revolutionary work of twentieth century philosophy. Though Heidegger radically revised phenomenology, he still considered himself a phenomenologist. With him, phenomenology became existential phenomenology, which focused on producing a "hermeneutics of facticity" – an interpretation of the human condition as lived by real human beings. Heidegger was followed in this effort most famously by Jean-Paul Sartre in his book Being and Nothingness, which carried Heidegger's analysis further and applied it to concrete situations. Maurice Merleau-Ponty critiqued Sartre while still continuing on the path marked by Heidegger's emphasis on our practical engagement with the world as opposed to the Husserlian focus on explicit conscious awareness. The hermeneutical strand of Heidegger's work was developed by Hans-Georg Gadamer in Truth and Method. Together, hermeneutics – the theory of interpretation in the most general sense – and phenomenology constitute the main concerns of continental philosophy. These concerns tend to require a great deal of systematic thinking to make progress in them, and thus continental philosophy tends to look more often at the "big picture" and to deal more directly with everyday human concerns than does analytic philosophy – though like any stereotype, this generalization admits of many exceptions and should not be read to the letter.