Here is a brief glossary of a few philosophical terms that I threw together. It took me ages to finally remember what these all mean, so hopefully this will be helpful for someone. As I said, at the moment it's very short, but I hope to expand it over time.

A Posteriori: A type of knowledge, gained by induction. That is to say, that this knowledge is gained from experience (a posteriori literally means after experience). For example, by observing that the sun has always risen in the morning in the past, we come to the a posteriori conclusion that it will always rise.

A Priori: Knowledge gained before experience (deductively). For example, a shape which is both a perfect square and a perfect circle at exactly the same time is impossible, this we know before even having experience of attempting to draw such an object.

Cartesian: Follower of Descartes' ideas.

Deduction: The process of gaining knowledge independently of experience, through pure logical reasoning. This knowledge is deductive knowledge, or a priori knowledge. Of the spheres of human reasoning, only mathematics can truly be said to be deductive.

Deism: The belief that there is a God who created the universe, but that after creating it he left it to regulate itself and doesn't step in to provide miracles or the like.

Dualism: Dualists believe that the world consists of both mental and physical objects, like minds and bodies respectively. Most of the major philosophers, including Descartes and Locke, were dualists.

Empiricist: One of the two main schools of philosophical thought throughout history. Empiricists believed that pure reasoning alone was not sufficient to gain knowledge of the world, but experience was also required. Empiricists started with Aristotle, and include Locke, Berkeley and Hume.

Existentialism: Popular in the last century, the belief that existence comes before essence, that is, that who you are is only determined by you yourself, and not merely an accident of birth. Sartre is the most famous existentialist. It is in part a reaction to the ideas of Hegel and Nietzsche.

Idealist: An idealist is someone who believes that existence is not truly physical at all, but mental. Berkeley is the most famous idealist, and claimed that nothing was real except our minds and God, and everything else was just ideas in those minds. Leibniz also may have been an idealist, but this isn't that clear from his writings.

Induction: The process of gaining knowledge through experience. Hume argued highly convincingly that induction proves nothing for certain, and therefore deductive, or a priori knowledge, is highly prized over inductive, or a posteriori knowledge by philosophers. As may have occurred to you already, all scientific knowledge, relying as it does on experiments - experience in other words - is inductive and therefore uncertain.

Innate Ideas: For centuries philosophers and the intelligentsia at large believed in innate ideas/knowledge, that is, knowledge we are born knowing, put there by God. Usually various moral precepts like repugnance for murder were cited as being innate. I guess we might call them instincts nowadays. Locke mounted a devastating attack on innate ideas in his An Essay Concerning Human Understanding, and since the philosophers preceding and following him had little enthusiasm for them either, they lost popularity.

Master/Slave Morality: Nietzsche's terms for two kinds of morality. In the State of the Nature there were Masters, the strong, proud, cruel, courageous etc, and the Slaves, the weak, humble, compassionate, cowardly, etc. In envy of the Master's powers, the Slaves overthrew them and rose to the dominance they enjoy in Christianity and Judaism today. Master and Slave moralities are simply the judgement of good being attached to one attributes of one of the two groups. Slave morality, for example, is the view that being humble, compassionate etc is good.

Materialist/Physicalist: The opposite of idealists, materialists claim that the mental is just an illusion produced by the entirely physical brain, and only the physical is real.

Monotheism: The belief in one true God. Christianity, Judaism and Islam are all examples of religions based on this belief.

Occasionalism: Malebranches' idea on how the mind and body could interact - namely, that naturally they didn't, and God had to intervene to allow the soul to affect the physical world each and every time you do something. Now justly considered ludicrous.

Ontology: A branch of metaphysics, the study of the nature of being. What is existence, and so on.

Pantheism: The belief that the universe is 'God'. Spinoza was a pantheist. Pantheists usually don't think the universe is conscious, but they often worship it. Ancient religions were often pantheistic.

Polytheism: The belief in more than one God, for example Hinduism or the religion of the Ancient Greeks or Romans.

Pragmatism: A view put forward at the turn of the 19th/20th century, that only those issues that would make a difference should be debated - if it won't make a difference either way, why even bother considering it? William James was a famous proponent.

Pre-established Harmony: The idea, put forward by Leibniz, that the soul and body don't interact at all, instead God set them up at creation to act in perfect harmony.

Rationalist: The other main school of philosophical thought. Rationalists believe that reason alone is sufficient to gain knowledge of the world. Rationalists started with Plato, and include Descartes, Leibniz and Spinoza. The current thought is that Kant collapsed the two schools of Rationalists and Empiricists into each other, destroying the distinction. I don't really agree with this, and think it still applies today, albeit perhaps to a lesser extent.

Scholastics: Catholic philosophers, usually monks, who dominated western philosophy from St Augustine in the 4th century until the early 16th Century, when Descartes started the process of overthrowing them. St Aquinas is considered to be the greatest of them.

Social Contract: A theory on how government and societies began. Contractarians hold that societies were formed by the consent of the populations of various areas who decided, for whatever reasons (these vary from philosopher to philosopher) that it would be to their mutual advantage to band together and cooperate.

State of Nature: Before governments and societies were formed, humans lived in the state of nature, where it was every man for himself. Accounts of what this was like vary according to who you read. It means more or less the stone age period.

Substratum: An opinion on substance (the stuff the universe is made of), particularly held by Locke, that substance was that which had no properties itself, but lay underneath properties, like solidity, heat, colour, etc, and supported them. The substratum of a table, for example, supports its colour, solidity and shape.

Syllogism: An ancient form of a logical argument, first put forward by Aristotle. A syllogism typically consists of three sentences; two premises, one conclusion. If the premises were true, the conclusion must be true. For example: all left-handed people are smokers. Ann is left-handed. Ann must be a smoker.

Tabula Rasa: A blank slate. Locke claimed that as opposed to the mind being imprinted with innate ideas before birth, in actually the mind was a blank slate, tabula rasa, when born, and all knowledge was gained first from our experience of the world, and later by our reasoning. This view is popular today.

Teleology: Teleological explanations attempt to explain things in terms of their function. For example, Leibniz sought to explain the existence of evil in the world by arguing that it was necessary for free-will to exist.

Theism: The belief that there is a God of some description. Covers a wide variety of religious beliefs, obviously.

Utilitarianism: The view that an action is good in proportion to the amount of people it produces happiness in, and in proportion to how much happiness it produces in them. The greatest good for the greatest number of people is the best action therefore. Bentham and J.S. Mill are famous Utilitarianists.