Philosophical terms glossary
A posteriori: Knowledge that can only be acquired from experience of the external world. For example, there is no way you could work out what temperature water boils at purely by thinking. You’d have to have experience of the external world to know the answer.
The opposite word: a priori
A priori: Knowledge that can be acquired without experience of the external world, through thought alone. For example, you can work out what 900 divided by 7 is purely by thinking – you don’t need experience of the external world to verify it.
The opposite word: a posteriori
Abductive argument: A form of inductive argument which shows says that something is probably true because it is the best explanation. An explanation might be considered better than alternatives due to its explanatory and predictive power, or because it makes the fewest assumptions (a principle known as Ockham’s razor).
Ability knowledge: Knowledge of how to do something. For example, knowing how to ride a bike or how to juggle.
Related: acquaintance knowledge, propositional knowledge
Acquaintance knowledge: Knowledge of something or someone. For example, “I know James well” or “I know Berlin well”.
Related: ability knowledge, propositional knowledge
Analytic reduction: If X analytically reduces to Y, then the meaning of X is the same as the meaning of Y. For example, “triangle” analytically reduces to “3-sided shape” because the meaning of “triangle” is “3 sided shape”.
Analytic truth: A proposition that is true in virtue of the meaning of the words. For example, “A bachelor is an unmarried man” or “triangles have 3 sides” or “1+1=2”. Denying an analytic truth results in a logical contradiction. For example, the idea of a married bachelor or a 4-side triangle is a contradiction – it doesn’t make sense.
The opposite word: synthetic truth
Antecedent: The first part of a conditional statement such as “if A then B”. In this example, the antecedent is “if A…”. The second part of the conditional statement (i.e. “…then B”) is known as the consequent.
The opposite word: consequent
Apophatic way: See via negativa.
Arête: An ancient Greek word used by Aristotle to describe a property or virtue that enables something to achieve its ergon (function). For example, the arête of sharpness enables a knife to achieve its function (to cut things).
(Hard) Behaviourism: The view that propositions about mental states can be (analytically) reduced without loss of meaning to propositions about behaviours using the language of physics. For example, the word “pain” means nothing more than the actual physical states and behaviours associated with pain.
(Soft) Behaviourism: The view that propositions about mental states are propositions about behavioural dispositions. For example, the statement “he was in pain” means both actual physical states and behaviours (e.g. saying “ouch!”) and behavioural dispositions (e.g. if you asked him “did that hurt?” he would have a disposition to respond “yes”).
Blik: An unfalsifiable belief that is held in the face of conflicting evidence, but that is nevertheless meaningful.
Cataphatic way: See via positiva.
Categorical imperative: A statement about what you should do that is not conditional on anything. According to Kant, the categorical imperative we should all follow is to “act only according to that maxim whereby you can at the same time will that it should become a universal law without contradiction”.
Cognitive statement: Cognitive statements aim to literally describe how the world is and are either true or false. For example, “water boils at 100°c” , “triangles have 3 sides”, “Paris is the capital of France”, and “London is the capital of France” are all cognitive statements because they are capable of being true or false.
The opposite word: non-cognitive statement
Consequent: The consequent is the second part of a conditional statement such as “if A then B”. In this example, the consequent is “…then B”. The first part of the conditional statement (i.e. “if A…”) is known as the antecedent.
The opposite word: antecedent
Consequentialist: An ethical theory that values as actions as good or bad according to their consequences. For example, utilitarianism is a consequentialist ethical theory.
Contingent truth: Something that is true but that might not have been true. For example, “Paris is the capital of France” is a contingent truth because they could have made Lyon the capital instead. Even “water boils at 100°c” is a contingent truth because the laws of physics could have been different.
The opposite word: necessary truth
Contradiction: Two claims contradict one another if they cannot both be true simultaneously. For example, “today is Monday” contradicts the claim “today is not Monday”.
Contradiction in conception: A maxim leads to a contradiction in conception if it would somehow be self-contradictory for everyone to follow it. For example, if everyone followed the maxim “to steal” then it wouldn’t even be possible to steal because there would be no private property.
Contradiction in will: A maxim leads to a contradiction in will if you cannot rationally will that everyone follow it. For example, you cannot rationally will the maxim “never help people in need” if you yourself expect other people to help you when you’re in need.
Deduction: A method of deriving true propositions from other true propositions (using reason and logical necessity). It is an a priori method of gaining knowledge.
Deductive argument: An argument where the premises are intended to logically guarantee the conclusion (i.e. an argument that is intended to be logically valid). For example, the logical problem of evil is supposed to logically guarantee the conclusion “God does not exist” whereas an inductive argument such as the evidential problem of evil is only supposed to provide evidence to supports its conclusion.
The opposite word: inductive argument
Deontological ethics: Ethical theories that focus on duty, or what must be done. For example, Kant says we have a duty to follow the categorical imperative.
Direct realism: The view that a mind-independent external world exists and that we perceive it directly.
Disjunction introduction: The logical principle that if the statement “P” is true, then the statement “P or Q” must also be true.
(Ordinary) Doubt: Being unsure whether something in your everyday life is true. For example, you might doubt whether you locked the door when you left the house and so doubt whether your belief “I locked the door” is true.
Related: scepticism
(Philosophical) Doubt: Being unsure whether anything you believe is true. For example, you might doubt your perceptions and your own thoughts (and thus any beliefs formed from them) because of the possibility of global sceptical scenarios.
Related: scepticism
(Substance) Dualism: The view that minds can exist completely separately from physical bodies. In other words, there are two different kinds of substance: physical bodies and non-physical minds.
(Property) Dualism: The view that physical substances can have non-physical mental properties. These mental properties are neither reducible to nor supervenient upon physical properties.
Eliminative materialism/Eliminativism: The view that our common sense understanding of mental states (folk psychology) is radically mistaken and that some or even all of these mental states don’t exist and should be eliminated in favour of more accurate neuroscientific alternatives.
Emotivism: The metaethical view that moral judgements express (non-cognitive) emotional attitudes. For example, according to emotivism, ‘murder is wrong’ means something like “boo! Murder!”.
Empiricism: Empiricism can mean different things depending on what it is contrasted against:
Contra rationalism, empiricism says all knowledge of synthetic truths is acquired a posteriori.
Contra innatism, empiricism says there is no such thing as innate knowledge and that all (propositional) knowledge is acquired after we are born.
Epiphenomenalism: A form of dualism that says that the mental and physical interact in only one direction: From physical to mental. For example, getting hit in the (physical) head causes the mental state of pain, but my mental state of pain don’t cause anything itself. Instead, it’s just the (physical) brain state that causes me to rub my (physical) head and say “ouch!”.
Related: interactionism
Ergon: An ancient Greek word used by Aristotle to describe the function or characteristic activity of a thing. For example, the ergon of a knife is to cut things.
Error theory: The metaethical view that moral judgements express cognitive statements but that moral properties don’t exist and so all moral judgements are false. For example, “murder is wrong” is false because “wrongness” doesn’t exist as a property.
Eudaimonia: An ancient Greek word used by Aristotle to describe the good life for a human being in the broadest sense. It is sometimes translated to “human flourishing”. Eudaimonia is an objective property of a person’s whole life and is the final end for humans.
Eternal: God is said to be eternal if He exists outside of time.
Everlasting: God is said to be everlasting if He exists within time but is without beginning or end.
Fallacy: The use of invalid or otherwise faulty reasoning.
Falsifiable: A belief or proposition that is incompatible with some possible observation. For example, “water boils at 100°c” is falsifiable because it incompatible with the observation of heating some water to 999°c and it not boiling. In contrast, an unfalsifiable proposition is compatible with every possible observation, and is thus said to be meaningless.
Felicific calculus: Bentham’s formula for calculating net pleasure and thus for deciding the correct course of action according to act utilitarianism.
Final end: Something that is valuable in itself. You do not need to give further reason why it is valuable – it is valuable for its own sake.
Folk psychology: Our common-sense our understanding and model of the mind and mental states. For example, ‘happy’, ‘sad’, ‘pain’, and ‘belief’ are all folk-psychological concepts.
Functionalism: The view that mental states can be characterised by their functional role within a cognitive system. For example, a functionalist might say that pain is an unpleasant mental state that creates a desire for it to stop and that causes the organism to get away from the thing that’s causing it harm. The functional role of pain are multiply realisable: an octopus, an alien, and a human can all feel pain.
Gettier case: An example of a justified true belief that is not knowledge. Gettier cases thus show that the tripartite definition of knowledge does not provide sufficient conditions for knowledge.
Good will: To be motivated by and choose your actions for the sake of duty, according to Kant.
Hume’s Fork: David Hume’s claim that there are only two judgements of reason: relations of ideas (i.e. the opposite is inconceivable to the mind and so can be known a priori) and matters of fact (i.e. the opposite is conceivable and so can only be known a posteriori).
Hypothetical imperative: A statement about what you should do if you want to achieve a certain outcome. For example, “you should leave now if you want to get to the station in time”.
Idealism: The view that there is no such thing as a mind-independent external world and that what we perceive are mind-dependent ideas.
Indirect realism: The view that a mind-independent external world exists, but that we perceive it indirectly via sense data. This sense data is caused by and represents the mind-independent external world.
Inductive argument: An argument where the premises support the conclusion, but don’t logically guarantee it. For example, the evidential problem of evil is supposed to provide good evidence for the conclusion “God does not exist”. However, unlike a deductive argument, an inductive argument does not logically guarantee its conclusion.
The opposite word: deductive argument
(Leibniz’s law of) Indiscernibility of identicals: The principle that if A and B are the same thing, then A and B must have all the same properties. In other words, if two things have different properties, then they can’t be the same thing. For example, “that can’t be Smith’s car because Smith’s car is silver and that car is red”.
Infallibilism: The definition of knowledge as true belief that is certain. According to infallibilism, anything that can be doubted is not knowledge. For example, on the infallibilist definition, I can’t know “grass is green” because I might be being deceived by an evil demon.
Innatism: The view that there is some (propositional) knowledge that we are born with. Plato, for example, argues that humans have innate knowledge of geometry and attempts to show this with his slave boy example.
The opposite word: empiricism
Intentionality: The ability of mental states to be about or directed towards a subject. For example, you can have a thought about a frog, a belief about the moon, or a desire to drink beer (in this case, the mental state is directed at the beer – it is about beer).
Interactionism: A form of dualism that says that the mental and physical can interact in both directions. For example, getting hit in my (physical) head causes the mental state of pain, and my mental state of pain causes me to rub my (physical) head and say “ouch!”.
Related: epiphenomenalism
(Rational) Intuition: The ability to know something is true just by thinking about it. It is an a priori method of gaining knowledge.
Invalid argument: An argument where it’s possible for the premises to be true but the conclusion be false. For example, even though 1, 2, and 3 below are true, the following argument is invalid:
1. If Socrates is a man, then Socrates is a mortal
2. Socrates is a mortal
3. Therefore, Socrates is a man
Even though both premises (1 and 2) are true, and the conclusion (3) is also true, this argument is not valid because it’s possible for the premises to be true and the conclusion to be false. For example, if Socrates was the name of my cat, then premise 2 (Socrates is a mortal) would still be true but the conclusion (Socrates is a man) would be false.
The opposite word: valid argument
(False) Lemma: A (usually minor) premise in an argument. A false lemma is thus a false premise in an argument.
Materialism: See physicalism.
Maxim: A rule or law that you follow. For example, “not to steal”.
Moral realism: The metaethical view that that mind-independent moral properties (e.g. good, bad, right, and wrong) and facts exist.
The opposite word: moral anti-realism
Moral anti-realism: The metaethical view that that mind-independent moral properties (e.g. good, bad, right, and wrong) and facts do not exist.
The opposite word: moral realism
Multiple realisability: Something is multiply realisable if there are many different things it can be. The claim that mental states are multiply realisable presents a challenge for behaviourism and type identity theory:
Mental states can be realised through many different behaviours, which is a problem for the behaviourist claim that mental states are behavioural dispositions. For example, someone in pain may say “ouch!”, but they may not if they don’t want to look like a wimp.
Against type identity theory, mental states can be realised by many different physical things. For example, a human, an octopus, can all feel pain but they each have physically different brains.
(Moral) Naturalism: The metaethical view that moral judgements express cognitive statements and that these cognitive statements are true or false in virtue of natural properties. For example, “murder is wrong” is true because “wrongness” is some natural property of the act of murder (e.g. it causes pain).
Naturalistic fallacy: G.E. Moore’s phrase for the alleged philosophical mistake of reducing moral properties (e.g. good) to natural properties (e.g. pleasure).
Necessary condition: A condition that something must meet to be part of a concept. In other words, if anything that does not have this condition it will not be part of that concept. For example, “unmarried” is a necessary condition of “bachelor” because you have to be unmarried to fit the concept of a bachelor.
Related: sufficient conditions
Necessary truth: Something that must be true (in all possible worlds). For example, “1+1=2” and “it is impossible for both a and not a to be true” are necessary truths because there is no possible world in which they are false.
The opposite word: contingent truth
(Moral) Nihilism: The view that moral values do not exist and thus there is no reason to justify or condemn behaving in one way over another.
Non-cognitive statement: Non-cognitive statements do not aim to describe how the world is and so are not capable of being either true or false. For example, “ouch!”, “boo!”, “hooray!”, “don’t do that!”, and “shut the door please” are all examples of non-cognitive statements because they are not capable of being true or false.
The opposite word: cognitive statement
(Moral) Non-naturalism: The metaethical view that moral judgements express cognitive statements and that these cognitive statements are true or false in virtue of non-natural properties. For example, “murder is wrong” is true because the act of murder has the non-natural property of “wrongness”. Such moral properties are basic in that they cannot be reduced to anything simpler.
Ockham’s razor: The principle that if two theories have the same explanatory and predictive power, the theory that invokes the fewest entities is usually the better one. In other words, the simplest explanation is the best (all else being equal).
Omnibenevolent: Perfectly good, i.e. nothing can be more good.
Omnipotent: Perfectly powerful, i.e. nothing can be more powerful.
Omniscient: All-knowing, i.e. nothing more can be known by an omniscient being.
Ontological reduction: If X ontologically reduces to Y, then X and Y are the same thing but “X” does not automatically mean the same thing as “Y”. For example, although water ontologically reduces to H2O, it’s possible that someone could not know this: they might know the proposition “there is water in the lake” and yet not know “there is H2O in that lake” because the meaning of these two propositions is different.
Phenomenal knowledge: Knowledge of qualia is sometimes called phenomenal knowledge – i.e. knowledge of what it is like to have a certain experience.
Phronesis: An ancient Greek word used by Aristotle to describe practical wisdom. Someone who has phronesis possesses virtues that provide a general understanding of good that enables them to think through, understand, and act virtuously. For example, they would be funny or angry or sad when the situation is right but never at an inappropriate time or in an inappropriate way.
Physicalism: The view that everything is physical or supervenes on the physical (e.g. properties and events supervene on the physical).
Prescriptivism: The metaethical view that moral judgements express (non-cognitive) prescriptive instructions that primarily aim to guide behaviour. For example, according to prescriptivism, “murder is wrong” means something like “don’t murder people!”.
Propositional knowledge: Knowledge that something is true. For example, “I know that London is the capital of England.”
Related: ability knowledge, acquaintance knowledge
Qualia: The subjective qualities of experience – i.e. what something feels like inside your mind. Qualia are not properties of objects themselves, but properties of our experience of objects. Examples of qualia include the redness of my experience when I look at a ripe tomato and the taste I experience when I drink beer.
Rationalism: The view that there are some synthetic truths that can be known purely through a priori means. For example, Descartes’ cogito argument attempts to prove the synthetic truth “I exist” using thought alone and without reference to the external world.
The opposite word: empiricism
Realism: Realist theories claim that certain kinds of mind-independent entities exist. In metaethics, for example, moral realism claims that mind-independent moral properties exist. And in knowledge from perception, direct realism and indirect realism claim that mind-independent objects exist.
Reliabilism: The definition of knowledge as true belief informed via a reliable method. For example, if I have good eyesight and see a car in the distance, my true belief “that’s a car” is knowledge according to reliabilism because it is informed via a reliable method (my eyesight).
(Global) Scepticism: A belief that it is impossible to know anything because of the possibility of global sceptical scenarios. For example, “I might be dreaming, in which case I can’t know today is Monday”, or “I might be a brain in a vat, so I can’t know that I’m currently reading a book”. Global sceptical scenarios undermine our ordinary justifications and thus cast doubt on all our ordinary knowledge.
(Local) Scepticism: A belief that it is impossible to know anything within a particular area. For example, you might be a theological sceptic in which case you believe it is impossible to know anything about God’s existence or character, or you might be a moral sceptic and believe it is impossible to acquire knowledge of moral truth.
Solipsism: The view that your own mind is the only thing that exists.
Sound argument: A valid argument with true premises (and thus a true conclusion).
Sufficient conditions: Conditions that, if all are met, guarantee that something is part of a concept. For example. “unmarried” and “man” are sufficient conditions of “bachelor” because everything that is an unmarried man is a bachelor. Being an unmarried man is sufficient to be a bachelor – you don’t need to meet any other conditions.
Related: necessary condition
Spatial order: Examples of organisation/order within the universe. For example, an eye is a complex organisation of matter that enables vision, and a watch is a complex organisation of matter that enables people to tell the time.
Related: temporal order
Supervenience: X supervenes on Y if a change in Y is necessary for a change in X. This is mainly relevant in the discussion of property dualism: Property dualism says mental properties do not supervene on physical properties and so it is possible for two physically identical things to have different mental properties.
Synthetic truth: A proposition that is true in virtue of how the world is. For example, “grass is green” or “water boils at 100°c”. Unlike an analytic truth, denying a synthetic truth does not lead to a logical contradiction. For example, even though “grass is green” is true, there is no logical contradiction in the idea of red grass. The idea of red grass makes sense, even if it is not how the world actually is.
The opposite word: analytic truth
Tabula rasa: Latin for “blank slate”. It is how Locke describes the mind at birth.
Tautology: A statement that says the same thing twice and thus is trivially true. For example, “red is red”.
Temporal order: Examples of organisation/order of the laws of the universe. For example, the laws of gravity and electromagnetism are examples of temporal order because if they were different life would not be able to form within the universe.
Related: spatial order
Theodicy: An explanation of why an omnipotent and omnibenevolent God would allow the existence of evil. In other words, a theodicy is a response to the problem of evil.
Tripartite definition of knowledge: The definition of (propositional) knowledge as justified true belief.
Type identity theory: The view that mental states are identical to (ontologically reduce to) brain states. For example, type identity theorist might say that the mental state of pain is identical to c-fibers firing.
(Act) Utilitarianism: The ethical theory that happiness is good and that morally correct actions are those that maximise happiness and minimise pain.
(Rule) Utilitarianism: The ethical theory that happiness is good and that we should follow general rules that maximise happiness and minimise pain (even though there may be specific instances where following these rules does not maximise happiness).
(Preference) Utilitarianism: The ethical theory that morally correct actions are those that maximise people’s preferences.
Valid argument: An argument where if the premises are true, the conclusion must also be true. For example, it is logically impossible for 1 and 2 below to be true but 3 be false:
1. If Socrates is a man, then Socrates is a mortal
2. Socrates is a man
3. Therefore, Socrates is a mortal
Note: A valid argument does not necessarily mean the conclusion is true. Even though the logic of the argument may be valid, the premises (and thus the conclusion) may be false.
Value judgement: A statement about whether something is good, bad, right, or wrong.
Verification principle: A.J. Ayer’s claim that a statement can only be meaningful if it is either an analytic truth or empirically verifiable.
Via negativa: The view that the only way to accurately describe God is to describe what God is not. For example, rather than describing God as ‘powerful’, the via negativa would say God is ‘not weak’.
The opposite word: via positiva
Via positiva: The view that we can describe in positive terms what God is. For example, we can describe God as ‘good’ and ‘powerful’ rather than simply ‘not evil’ and ‘not weak’.
The opposite word: via negativa
Virtue epistemology: Definitions of knowledge that invoke intellectual virtues. Intellectual virtues are things like caring about the truth and thinking rationally. Zagzebski’s definition of knowledge, for example, says knowledge is belief that arises from an act of intellectual virtue.
Virtue ethics: Ethical theories that focus on what a good person is rather than what good actions are. For example, Aristotle’s ethics talks about virtues and vices of character and how this relates to being a good person and achieving eudaimonia.
(Philosophical) Zombie: A being in another possible world that is physically identical to an ordinary human in every way but lacks qualia. For example, the zombie version of you would have exactly the same brain states and behaviours as you but would not have the corresponding phenomenal experience/qualia.