231 terms
Glossary
Every technical word on this site, defined plainly. Underlined terms anywhere on the site link here; hover over them to see the definition in place.
A
- A priori and a posteriori
Knowledge is a priori if it can be had independently of experience, like knowledge of arithmetic, and a posteriori if it depends on experience, like knowledge that it is raining.
- A-theory of time
The view that time really passes: there is an objective present, and events genuinely move from future to present to past. Opposed to the B-theory of time.
On the A-theory, it is a real fact about the world, not just about your perspective, that now is now.
- Ability hypothesis
A physicalist reply to the knowledge argument: when Mary first sees red, she gains no new fact, only new abilities, to recognise, remember and imagine red.
Proposed by Laurence Nemirow and developed by David Lewis.
Appears in Mary's room
- Absurdism
The view, associated with Albert Camus, that the human search for meaning meets a silent universe, and that the right response is to live in full awareness of this rather than escape it.
- Affirmation (of life)
In Nietzsche, saying yes to one's life as a whole, including its suffering, so completely that one would will it to recur exactly as it was.
Appears in Would you live your life again, forever?
- Amor fati
Latin for 'love of fate'. Nietzsche's ideal of wanting nothing to be different, not merely bearing what happens but loving it.
- Anatta (not-self)
The Buddhist teaching that there is no permanent, unchanging self; a person is a changing stream of physical and mental processes.
- Animalism
The view that each of us is a human animal, so that personal identity over time is the persistence of a biological organism, not of memories or psychology.
- Anthropic reasoning
Reasoning that takes into account the fact that we exist to make an observation. For example, we should not be surprised to find the universe compatible with life, since we could not observe one that was not.
Wikipedia · Are we living in a simulation?, The Fermi paradox
- Apatheia
The Stoic ideal of freedom from destructive passions such as fear, anger and craving. It is not indifference or numbness, but a calm based on correct judgement.
- Appearance and reality
The distinction between how things seem to us and how they really are. Much of philosophy, from Plato's cave to the brain in a vat, turns on whether and how we can cross that gap.
Appears in Plato's cave
- Authenticity
In existentialism, living according to choices one recognises as one's own, rather than hiding behind roles, conventions or excuses.
B
- B-theory of time
The view that there is no objective present or flow of time. Events are simply earlier than, later than or simultaneous with one another, and 'now' is like 'here'. Usually paired with eternalism.
- Backward induction
Reasoning from the last step of a sequence backwards to the first, ruling out options one at a time. It drives the unexpected hanging paradox and many results in game theory.
- Bad faith
Sartre's term for self-deception about our own freedom: pretending that we are fixed things, determined by roles or circumstances, in order to avoid responsibility for our choices.
Sartre's example is a café waiter who plays at being a waiter as if he had no choice.
- Bayesianism
The view that rational belief comes in degrees, measured as probabilities, and that we should update those degrees on new evidence according to Bayes' theorem.
Wikipedia · Why trust that the future will be like the past?
- Biological naturalism
John Searle's view that consciousness is a real, subjective biological phenomenon caused by brain processes, as digestion is caused by the stomach, and that running a program cannot by itself produce it.
Wikipedia · Could a machine be conscious?, Could you upload your mind?
- Block universe
The picture, suggested by relativity, of past, present and future as equally real parts of a single four-dimensional spacetime, with no moving present.
- Boltzmann brain
A hypothetical self-aware brain that forms by a random fluctuation out of disorder, complete with false memories. Some cosmological models predict such brains should vastly outnumber ordinary observers.
- Borderline case
A case where it is unclear whether a vague word applies, such as whether a man with a certain number of hairs is bald.
Appears in The sorites paradox
- Bounded utility
The view that there is an upper limit to how good any outcome can be for a person, so that no promised reward can be large enough to outweigh every tiny probability.
Appears in Pascal's mugging, The St. Petersburg paradox
- Branch-line case
Derek Parfit's variant of the teleporter in which the original survives for a short while alongside the replica, forcing the question of which, if either, is you.
Appears in Would you step into the teleporter?
- Branching timeline
A model of time travel in which changing the past creates a new, separate history, so the traveller's original past remains intact elsewhere.
Appears in The grandfather paradox
- Brute fact
A fact that has no explanation; it is simply so. Whether the existence of the universe is a brute fact is a central question in cosmological arguments.
- Bundle theory
The view, classically stated by David Hume, that the self is nothing over and above a bundle of perceptions, thoughts and feelings, with no further owner.
C
- Cartesian circle
The charge that Descartes argues in a circle: he uses clear and distinct ideas to prove that God exists, then relies on God to guarantee that clear and distinct ideas are reliable.
- Categorical imperative
Kant's supreme principle of morality, a command that binds everyone regardless of their desires. In one form: act only on a rule you could will to be a universal law. In another: treat humanity always as an end, never merely as a means.
- Causal closure of the physical
The principle that every physical event that has a cause has a sufficient physical cause. If true, it leaves no obvious room for a non-physical mind to make a difference.
- Causal decision theory
The theory that you should choose the act whose effects you expect to be best, ignoring correlations your choice does not cause. It recommends taking both boxes in Newcomb's problem.
- Causal loop
A chain of events that causes itself, such as an object or piece of information carried back in time that becomes its own origin.
- Causation
The relation between a cause and its effect. Philosophers disagree about whether it is a real necessary connection or, as Hume argued, just regular succession that we have learned to expect.
- Chaos (deterministic)
Behaviour of a fully deterministic system that is so sensitive to its starting conditions that long-term prediction is practically impossible.
Weather is chaotic: a tiny measurement error grows until forecasts beyond a couple of weeks are useless.
- Closed timelike curve
A path through spacetime that returns to its own past. Some solutions to Einstein's equations of general relativity allow them, which is why physicists take time travel puzzles seriously.
- Closure principle
The principle that if you know something, and know that it implies something else, you know that other thing too. Sceptical arguments often rely on it.
Wikipedia · How do you know anything at all?, Are you a brain in a vat?
- Coercion
Forcing someone to act by threat or pressure. Whether a coerced action is free, and whether the person is responsible for it, is a test case for theories of freedom.
Appears in Can you be free in a determined universe?
- Cogito
Short for 'cogito, ergo sum', I think, therefore I am. Descartes' claim that one thing survives all doubt: the existence of the one who is doubting.
- Cognitive instability
The property of a theory that, if believed, undermines your reasons for believing it. A cosmology predicting that you are probably a Boltzmann brain is said to be cognitively unstable.
Appears in Are you a Boltzmann brain?
- Compatibilism
The view that free will and moral responsibility are compatible with determinism. Freedom, on this view, is acting on your own reasons and desires without compulsion, not escaping the laws of nature.
Wikipedia · Is free will an illusion?, Can you be free in a determined universe?, Could you be responsible without any alternatives?
- Conceivability argument
An argument from the claim that something can be coherently imagined to the claim that it is possible. Zombie arguments against physicalism depend on it.
Appears in Could there be a zombie you?
- Confabulation
Producing a confident but false explanation of one's own behaviour or memories without intending to deceive. Split-brain studies offer famous examples.
Appears in Two minds in one head?
- Consequentialism
The family of moral theories holding that whether an act is right depends only on its consequences. Utilitarianism is the best-known member.
Wikipedia · What makes an action right?, The trolley problem
- Contextualism
In epistemology, the view that the standards for counting as 'knowing' shift with the context of conversation, so that the sceptic raises the standards rather than refuting ordinary knowledge.
- Contingent
True or existing, but able to have been otherwise. Opposed to necessary.
That you are reading this is contingent; that two plus two is four is not.
- Continuum
A space or quantity with no gaps, such as the real number line, in which between any two points there are infinitely many more.
D
- Decision theory
The formal study of how to choose rationally under uncertainty, usually by weighing outcomes by their probabilities and values.
- Decoherence
The process by which a quantum system's interaction with its environment makes interference between its possibilities practically undetectable, so that it appears to behave classically.
- Deduction
Reasoning in which, if the premises are true, the conclusion must be true. Contrasted with induction, which only makes its conclusion probable.
Wikipedia · Why trust that the future will be like the past?
- Demandingness objection
The objection that a moral theory, often utilitarianism, asks too much of us, for example by requiring us to give away nearly everything to help others.
- Deontology
The family of moral theories holding that some acts are required or forbidden in themselves, whatever their consequences, because of duties, rights or constraints.
Wikipedia · What makes an action right?, The trolley problem
- Deprivation account
The view that death is bad for the one who dies because it deprives them of the goods they would otherwise have had.
Appears in Should we fear death?
- Desert
Deserving something, such as praise, blame, reward or punishment, because of what one has done. 'Basic desert' is desert that does not depend on the good consequences of giving it.
Appears in Can anyone deserve blame?
- Desire-satisfaction theory
The theory that a person's life goes well to the extent that their desires, or the desires they would have if fully informed, are fulfilled.
Appears in Would you plug into the experience machine?
- Determinism
The thesis that the state of the world at any moment, together with the laws of nature, fixes everything that happens afterwards.
Wikipedia · Is free will an illusion?, Is the future already fixed?, Can you be free in a determined universe?, Are there other versions of you?, Could a perfect mind predict everything?
- Dialetheism
The view that some contradictions are true: some statements, such as the liar sentence, are both true and false.
- Dichotomy of control
The Stoic division of everything into what is up to us, our judgements, choices and desires, and what is not, everything else. Calm comes from caring only about the first.
- Difference principle
Rawls' principle that social and economic inequalities are just only if they work to the greatest benefit of the least advantaged members of society.
- Diminishing marginal utility
The principle that each additional unit of something, such as money, adds less value than the one before.
A thousand pounds matters far more to someone with nothing than to a millionaire.
- Doctrine of double effect
The principle that it can be permissible to cause a harm as a foreseen side effect of pursuing a good end, when it would be wrong to cause the same harm as a means to that end.
- Doing and allowing
The distinction between causing a harm and merely letting it happen. Many people think doing harm is worse than allowing it, even when the outcome is the same.
Appears in The trolley problem
- Dominance principle
The rule that if one option gives a better result than another whatever else is true of the world, you should choose it.
- Drake equation
A formula proposed by Frank Drake in 1961 that multiplies estimates such as the rate of star formation and the fraction of planets that develop life to estimate how many communicating civilisations exist in our galaxy.
E
- Effective altruism
A movement that uses evidence and careful reasoning to work out how to do the most good with a given amount of time or money, and then acts on it.
- Empiricism
The view that all or most knowledge comes from sense experience.
- Entropy
Roughly, a measure of disorder, or of how many microscopic arrangements are compatible with a system's large-scale state. In a closed system it tends to increase.
- Epiphenomenalism
The view that mental states are caused by physical states but have no effects of their own on the physical world, like the whistle of a steam engine.
Wikipedia · Why is there something it is like to be you?, Does your brain decide before you do?, Mary's room, Could there be a zombie you?
- Epistemic logic
The formal logic of knowledge and belief, which studies principles such as 'if you know that p, then p is true'.
- Epistemic luck
Luck that makes a belief true in a way that seems incompatible with knowing it. Gettier cases are the classic examples.
Appears in Is knowledge just justified true belief?
- Epistemicism
The view that vague words have perfectly sharp boundaries that we simply cannot know. There is an exact number of hairs at which a man becomes bald.
Appears in The sorites paradox
- Epistemology
The branch of philosophy that studies knowledge: what it is, how we get it, and how far it reaches.
- Error theory
In ethics, the view that moral statements try to state objective facts but are all false, because there are no such facts.
- Eternal recurrence
The idea that time is cyclical and every moment will repeat infinitely many times. Nietzsche used it mainly as a test of how fully one can affirm one's life.
- Eternalism
The view that past, present and future events all equally exist. Opposed to presentism.
- Eudaimonia
Greek for flourishing or living well. For Aristotle, the highest human good: an active life of reason and virtue over a complete lifetime.
Wikipedia · What makes an action right?, Does life have meaning without being given one?, Would you be good if no one could see?
- Evidential decision theory
The theory that you should choose the act which, if you learned you had done it, would be the best news about the outcome. It recommends taking one box in Newcomb's problem.
- Existence requirement
The principle that something can be good or bad for a person only if that person exists at the time. Epicurus relied on it to argue that death is not bad for the one who dies.
Appears in Should we fear death?
- Existentialism
A movement holding that human beings have no fixed nature or given purpose, and must create meaning through free choices for which they are wholly responsible.
Wikipedia · Does life have meaning without being given one?, Are you born with a nature?, Must we imagine Sisyphus happy?
- Expected utility
The value of an option calculated by weighting the utility of each possible outcome by its probability and adding the results. Standard decision theory says to maximise it.
- Expected value
The average result you would get if you repeated a gamble many times, found by multiplying each payoff by its probability and adding.
A fair coin paying £10 for heads and nothing for tails has an expected value of £5.
- Explanatory gap
Joseph Levine's term for the apparent impossibility of explaining why a given physical process should feel like anything at all from the inside.
Wikipedia · Why is there something it is like to be you?, What is it like to be a bat?
- Expressivism
The view that moral statements do not describe facts but express attitudes, such as approval or disapproval.
F
- Facticity
In existentialism, the given facts of a person's situation that they did not choose: body, past, birthplace, the world around them. Freedom always operates within facticity.
- Falsifiability
Karl Popper's criterion for a scientific theory: it must make predictions that could, in principle, turn out false.
Wikipedia · Why trust that the future will be like the past?, Is science the only path to truth?
- Fanaticism (in decision theory)
The property of a decision rule that lets any tiny probability of an enormous payoff outweigh any sure but moderate gain.
Appears in Pascal's mugging
- Fatalism
The view that what will happen will happen whatever we do, so that our choices make no difference to the outcome. Distinct from determinism, which says our choices are themselves causes.
- Fermi paradox
The conflict between estimates suggesting intelligent life should be common in our galaxy and the absence of any evidence of it.
- Flicker of freedom
A reply to Frankfurt cases: even when the agent cannot do otherwise, there remains a tiny alternative, such as starting to choose differently, which is enough to ground responsibility.
Appears in Could you be responsible without any alternatives?
- Forensic person
Locke's description of 'person' as a forensic term, a legal and moral notion concerned with responsibility, reward and punishment, rather than a biological one.
Appears in Are you your memories?
- Forms (Platonic)
In Plato, perfect, unchanging and non-physical realities, such as Beauty itself or Justice itself, of which the things we perceive are imperfect copies.
- Foundationalism
The view that knowledge has a structure like a building: some basic beliefs are justified without depending on others, and everything else rests on them.
Wikipedia · How do you know anything at all?, What if a demon deceived you about everything?
- Four-dimensionalism
The view that objects persist through time by having temporal parts, just as they extend through space by having spatial parts. A person is a 'spacetime worm'.
- Free will
The capacity to choose between options in a way that makes us the real authors of our actions and responsible for them. What exactly that requires is the central dispute.
Wikipedia · Is free will an illusion?, Does your brain decide before you do?, Buridan's donkey
- Free won't
Libet's suggestion that even if the brain starts preparing a movement before we decide, we can still consciously veto it at the last moment.
Appears in Does your brain decide before you do?
- Functionalism
The view that mental states are defined by what they do, their causal roles linking inputs, other mental states and behaviour, rather than by what they are made of.
Wikipedia · Is the mind just the brain?, Could a machine be conscious?, The Chinese room
G
- Gettier problem
The challenge, raised by Edmund Gettier in 1963, of explaining why a justified true belief that is true only by luck does not count as knowledge.
- Grandfather paradox
The apparent contradiction of travelling back in time and preventing your own birth, for example by stopping your grandparents from meeting.
- Great Filter
Robin Hanson's idea that some step on the road from dead matter to galaxy-spanning civilisation is extremely improbable, which would explain the silence of the sky.
H
- Hard determinism
The view that determinism is true and that it rules out free will and, on most versions, deserved praise and blame.
- Hard problem of consciousness
David Chalmers' name for the question of why physical processing in the brain is accompanied by subjective experience at all.
- Hedonism
In ethics, the view that pleasure is the only thing good in itself and pain the only thing bad in itself.
Wikipedia · Should we fear death?, Would you plug into the experience machine?
- Hierarchical theory of free will
Harry Frankfurt's view that you act freely when the desire that moves you is one you want to be moved by: when your first-order desires match your second-order desires.
Appears in Can you be free in a determined universe?
- Human nature
A set of traits, capacities or purposes that belong to all human beings as such. Existentialists deny there is a fixed one; Aristotle and many others build ethics on it.
I
- Identity over time
What makes something at one time the very same thing as something at another time, despite changes.
Appears in The Ship of Theseus
- Immortality
Living forever. Philosophers ask both whether it is possible and whether it would actually be desirable.
- Incompatibilism
The view that free will and determinism cannot both be true. Incompatibilists divide into libertarians, who keep free will, and hard determinists, who keep determinism.
- Indeterminism
The thesis that not every event is fixed by prior events and the laws of nature; some involve genuine chance.
Wikipedia · Is free will an illusion?, Is the future already fixed?, Could a perfect mind predict everything?
- Induction
Reasoning from observed cases to unobserved ones, such as from past experience to the future. Its conclusions are probable at best, never guaranteed.
Wikipedia · Why trust that the future will be like the past?
- Infinite series
The sum of infinitely many terms. Some such sums are finite: one half plus one quarter plus one eighth and so on adds up to exactly one.
- Intentionality
The 'aboutness' of mental states: the way beliefs, desires and perceptions are directed at or represent something beyond themselves.
- Is-ought gap
Hume's observation that conclusions about what ought to be cannot be validly drawn from premises only about what is, without some further step.
J
- Justification
Having good reasons or evidence for a belief, so that it is reasonable to hold.
Wikipedia · How do you know anything at all?, Is knowledge just justified true belief?
- Justified true belief
The traditional analysis of knowledge: you know something when you believe it, it is true, and you are justified in believing it. Gettier cases challenge it.
K
- Knowledge
In the sense philosophers usually study, knowing that something is the case. At minimum it requires true belief; exactly what else it needs is disputed.
- Knowledge argument
Frank Jackson's argument from Mary's room: someone could know every physical fact about colour and still learn something new on seeing red, so not all facts are physical.
L
- Laplace's demon
An imagined intellect that knows every particle's position and every force at one moment, and so could calculate the entire past and future. A symbol of determinism.
- Law of non-contradiction
The principle that a statement and its negation cannot both be true at the same time and in the same sense.
- Laws of nature
The basic regularities, or the principles behind them, that govern how the physical world behaves, such as the conservation of energy.
- Libertarianism (free will)
The view that we have free will and that free will requires indeterminism, so determinism is false. Unrelated to political libertarianism.
- Liberty of indifference
A will's supposed power to choose between options when it has no reason to prefer either, as in Buridan's donkey.
Appears in Buridan's donkey
- Limit (mathematics)
The value a sequence or sum approaches ever more closely as it goes on. Modern mathematics uses limits to make sense of infinite sums and motion.
M
- Maximin
A rule for choosing under uncertainty: pick the option whose worst possible outcome is better than the worst outcome of every alternative.
- Means and side effects
The distinction between harm you bring about as a way of achieving your goal and harm that is merely a foreseen by-product of achieving it. Central to the doctrine of double effect.
Appears in The trolley problem
- Measurement problem
The puzzle in quantum mechanics of why measurements yield single definite results when the theory's equations describe a superposition of all possible results.
- Mereology
The study of parts and wholes: when several things make up one thing, and whether a whole is anything over and above its parts.
- Metaethics
The branch of ethics that asks what moral claims mean, whether they can be true, and how we could know them, rather than which things are right or wrong.
- Metaphysics
The branch of philosophy that asks about the basic nature of reality: what exists, what time, causation and identity are, and why there is anything at all.
- Metastability
In electronics, an unstable in-between state a circuit can get stuck in when two inputs arrive almost simultaneously and it must decide between them. A real-world cousin of Buridan's donkey.
- Method of doubt
Descartes' strategy of setting aside every belief that can be doubted at all, in order to find something that cannot.
- Mind-body problem
The problem of how the mind, with its thoughts and feelings, is related to the body and brain.
- Moral distance
The question of whether physical or social distance makes any difference to our obligations to help someone.
Appears in The drowning child
- Moral luck
Cases where we judge people differently because of factors outside their control, such as two equally careless drivers, only one of whom happens to hit a child.
- Moral realism
The view that there are objective moral facts that hold independently of what anyone believes or feels.
- Moral relativism
The view that moral claims are true or false only relative to a culture or individual, with no standpoint-independent moral truth.
- Moral responsibility
Being the appropriate target of praise or blame for what one does.
Wikipedia · Can anyone deserve blame?, Could you be responsible without any alternatives?
- Moral status
Mattering morally for one's own sake, so that others have reasons to consider one's interests.
Appears in Do animals have moral rights?
- Multiple realisability
The idea that one kind of mental state, such as pain, could be produced by very different physical systems: human brains, octopus brains or perhaps silicon chips.
N
- Naive comprehension
The principle that for any condition, there is a set of exactly the things that meet it. Russell's paradox shows that it leads to contradiction.
Appears in Russell's paradox
- Narrative self
The view that a self is constituted, or at least shaped, by the story a person tells about their own life.
- Necessary being
A being that could not have failed to exist. Some arguments claim that only such a being can explain why anything contingent exists.
Appears in Why is there something rather than nothing?
- Nihilism
The view that life has no meaning or that there are no real values. In ethics, it can mean the denial that anything is truly right or wrong.
Wikipedia · Does life have meaning without being given one?, Would you live your life again, forever?, Must we imagine Sisyphus happy?
- Normative ethics
The branch of ethics that asks what we ought to do and what makes actions right or wrong, through theories such as utilitarianism, Kantian ethics and virtue ethics.
- Nothingness
The absence of anything at all. Some philosophers doubt the idea is even coherent; Sartre used it for consciousness's power to negate and step back from what is given.
- Numerical identity
Being one and the same thing, as opposed to being exactly alike. Twins may be qualitatively identical; only you are numerically identical to you.
Wikipedia · Are you the same person you were at eight?, The Ship of Theseus, Would you step into the teleporter?
O
- Object language and metalanguage
The distinction between a language being talked about (the object language) and the language used to talk about it (the metalanguage). Tarski used it to avoid the liar paradox.
- Objective list theory
The theory that some things, such as knowledge, friendship and achievement, make a life go better whether or not the person wants or enjoys them.
Appears in Would you plug into the experience machine?
- Objective value
Value that something has independently of anyone's attitudes towards it, as opposed to value it has only because someone cares about it.
- Ockham's razor
The principle that, other things being equal, the simpler explanation that posits fewer entities should be preferred.
- Ontology
The part of metaphysics that asks what kinds of things exist.
- Original position
Rawls' imagined situation in which people choose principles of justice from behind a veil of ignorance.
P
- Panpsychism
The view that consciousness, or something like it, is a fundamental and widespread feature of the physical world, present even in very simple things.
- Paradigm shift
Thomas Kuhn's term for a revolution in science in which one framework of theories, methods and assumptions is replaced by another.
- Paradox
An argument that seems to start from acceptable premises and proceed by acceptable reasoning to an unacceptable conclusion.
- Pascal's wager
Pascal's argument that, since the possible gain from believing in God is infinite and the cost finite, it is rational to believe even if God's existence is unlikely.
- Pattern identity
The view that a person is a pattern of information, so that whatever carries the same pattern, in any material, is that person.
Appears in Could you upload your mind?
- Personal identity
What makes a person at one time the same person as someone at another time.
Wikipedia · Are you the same person you were at eight?, Are you your memories?, Is the self an illusion?, Two minds in one head?, Would you step into the teleporter?
- Phenomenal concept
A concept of an experience that one can have only by having had the experience, such as the concept of what red looks like. Some physicalists use them to explain away Mary's new knowledge.
Appears in Mary's room
- Phenomenal consciousness
The felt, subjective aspect of experience: what it is like to see red, feel pain or taste coffee.
Appears in Why is there something it is like to be you?, Could a machine be conscious?, What is it like to be a bat?
- Philosophical suicide
Camus' term for escaping the absurd by a leap of faith or a system that promises a meaning beyond reason.
Appears in Must we imagine Sisyphus happy?
- Philosophical zombie
A hypothetical being physically identical to a person, behaving exactly the same, but with no conscious experience at all.
- Physicalism
The view that everything that exists is physical, or is fixed by the physical facts.
Wikipedia · Why is there something it is like to be you?, Is the mind just the brain?, What is it like to be a bat?, Mary's room, Could there be a zombie you?
- Posthuman
A hypothetical future being, descended from humans, whose capacities have been so extended by technology that it is no longer human in the ordinary sense.
- Potential infinity
Aristotle's notion of a process that can always be continued, such as counting, without an infinite totality ever existing all at once. Contrasted with actual infinity.
- Preferred indifferents
In Stoicism, things such as health and wealth that are naturally worth choosing but are not truly good, since one can live virtuously without them.
Appears in Should you only care about what you control?
- Presentism
The view that only the present exists; the past no longer exists and the future does not yet exist.
- Principle of alternative possibilities
The principle that a person is morally responsible for an action only if they could have done otherwise. Frankfurt cases are designed to refute it.
Wikipedia · Is free will an illusion?, Could you be responsible without any alternatives?
- Principle of bivalence
The principle that every statement is either true or false, with no third option. Vagueness and the liar paradox put it under pressure.
- Principle of indifference
The rule that, without any reason to favour one possibility over others, you should assign them equal probability.
- Principle of sufficient reason
The principle, championed by Leibniz, that everything that is the case has a reason or explanation why it is so and not otherwise.
Wikipedia · Why is there something rather than nothing?, Buridan's donkey, The bootstrap paradox
- Psychological continuity
Overlapping chains of memories, intentions, beliefs and character linking a person at different times. Many theories of personal identity are built on it.
Appears in Are you the same person you were at eight?, Are you your memories?, Would you step into the teleporter?, Could you upload your mind?
- Psychological egoism
The descriptive claim that people only ever act from self-interest, even when they appear to act for others.
Q
- Qualia
The qualities of conscious experiences as they feel from the inside, such as the redness of red or the painfulness of pain. Singular: quale.
Wikipedia · Why is there something it is like to be you?, What is it like to be a bat?, Mary's room
- Qualitative identity
Being exactly alike in every property, without necessarily being one and the same thing.
Wikipedia · Are you the same person you were at eight?, The Ship of Theseus
- Quasi-memory
A memory-like state of seeming to remember an experience, without the requirement that it was your own experience. Introduced to avoid circularity in memory theories of personal identity.
Appears in Are you your memories?
R
- Rationalism
The view that reason alone, independent of sense experience, is a major source of knowledge.
Wikipedia · Plato's cave, What if a demon deceived you about everything?
- Reactive attitudes
P. F. Strawson's term for emotions such as resentment, gratitude and indignation that we feel towards people we treat as responsible agents.
- Readiness potential
A slow build-up of electrical activity in the brain that begins before a voluntary movement, first recorded in 1965. Libet's experiments timed it against the reported decision to move.
- Reasons-responsiveness
A compatibilist account of responsibility: you are responsible if the mechanism behind your action would have responded to good reasons to act differently.
Appears in Can you be free in a determined universe?
- Relativity of simultaneity
The result from special relativity that whether two distant events happen at the same time depends on the observer's state of motion.
- Reliabilism
The view that a belief is justified, or counts as knowledge, if it is produced by a reliable process, one that usually produces true beliefs.
- Retributivism
The view that wrongdoers deserve punishment because of what they did, not only because punishing them has good effects.
- Rights
Entitlements that protect a person's interests or choices and constrain how others may treat them, even for the sake of a greater good.
- Risk aversion
Preferring a certain outcome to a gamble with the same or even higher expected value.
S
- Scientific realism
The view that our best scientific theories are approximately true, including what they say about unobservable things like electrons.
- Scientism
Usually a critical term for the view that science is the only source of real knowledge, or that every legitimate question is a scientific one.
- Second law of thermodynamics
The law that the total entropy of an isolated system never decreases over time. It underlies the difference between past and future in everyday life.
- Self
The subject of experience: the 'I' that thinks, feels and acts. Whether it is a thing, a process, a story or an illusion is disputed.
Wikipedia · Is the self an illusion?, Two minds in one head?, The grandfather paradox
- Self-consistency principle
Igor Novikov's principle that any events involving time travel must be consistent with each other, so that a time traveller cannot change the past, only take part in it.
- Self-reference
A sentence, set or system referring to itself. Many paradoxes, such as the liar and Russell's, arise from it.
Wikipedia · Could a perfect mind predict everything?, The liar paradox, The unexpected hanging, Russell's paradox
- Semantic externalism
The view that the meanings of our words, and the contents of our thoughts, depend partly on our environment, not only on what is in our heads.
- Semantics
Meaning: what words, sentences or symbols are about or stand for. Searle contrasts it with syntax.
- Sentience
The capacity to have experiences, especially of pleasure and pain.
- Set
In mathematics, a collection of things considered as a single object, defined by its members.
- Simulation hypothesis
The hypothesis that our world, including ourselves, is a computer simulation run by some more advanced civilisation.
Wikipedia · Are you a brain in a vat?, Are we living in a simulation?
- Skepticism
In philosophy, the view that we know much less than we think, or nothing at all, or the practice of doubting claims to knowledge.
Wikipedia · How do you know anything at all?, Are you a brain in a vat?, Plato's cave, What if a demon deceived you about everything?
- Speciesism
A term coined by Richard Ryder and made famous by Peter Singer for giving less moral weight to a being's interests simply because it is not human.
- Status quo bias
A tendency to prefer the current state of affairs simply because it is current.
- Stoicism
An ancient Greek and Roman school holding that virtue is the only true good and that peace of mind comes from distinguishing what is in our control from what is not.
- Strong AI
Searle's term for the claim that a suitably programmed computer would literally have a mind and understand, rather than merely simulate understanding.
- Subjectivity
The first-person point of view: the way the world is given to a particular subject. Kierkegaard held that some truths can only be grasped in it.
Appears in What is it like to be a bat?
- Substance dualism
The view that the mind is a non-physical thing, a separate substance from the body, though the two interact.
- Substrate independence
The assumption that a mind depends on the pattern of information processing, not on the material it runs on, so a mind could exist in silicon as well as in neurons.
Appears in Could a machine be conscious?, Could you upload your mind?, Are we living in a simulation?
- Supererogation
Acts that are good to do but go beyond what duty requires, such as heroic sacrifices.
- Superposition
In quantum mechanics, a state that combines several possible states at once, such as a particle described as being in many places, until it is measured.
- Supertask
An infinite sequence of tasks completed in a finite time, for example by doing each step in half the time of the one before.
- Supervaluationism
A theory of vagueness: a vague sentence is true if it comes out true on every acceptable way of making the vague word precise, false if false on all, and neither otherwise.
- Supervenience
One set of facts supervenes on another if there can be no difference in the first without a difference in the second.
If the mental supervenes on the physical, two physically identical people must have identical minds.
- Symbol grounding problem
The problem of how symbols in a system, such as words in a computer, come to mean anything, rather than just being linked to other meaningless symbols.
- Symmetry argument
Lucretius' argument that the endless time after our death is like the endless time before our birth, which we do not regret, so we should not fear death either.
Appears in Should we fear death?
- Syntax
The formal arrangement of symbols according to rules, regardless of what they mean. Searle argued that computers operate on syntax alone.
T
- The absurd
In Camus, the conflict between the human demand for meaning and the universe's silence in reply.
Wikipedia · Does life have meaning without being given one?, Must we imagine Sisyphus happy?
- Thought experiment
An imagined scenario used to test a theory or draw out an intuition, without needing to carry it out.
- Transitivity
A relation is transitive if, whenever A stands in it to B and B to C, A stands in it to C. Identity is transitive; similarity is not.
- Turing test
Alan Turing's proposed test for machine intelligence: if a judge holding text conversations cannot reliably tell a machine from a human, the machine passes.
- Type theory
A family of logical systems that sort objects into levels, or types, so that a collection can only contain things of a lower type. Russell devised it to block his paradox.
- Typicality assumption
The assumption that you should reason as if you are a typical member of the class of observers in your situation.
Appears in Are you a Boltzmann brain?
Ü
- Übermensch
Nietzsche's 'overhuman' or 'superman': an ideal of a person who creates their own values and affirms life completely.
U
- Uniformity of nature
The assumption that the future will resemble the past and unobserved cases will resemble observed ones. Hume argued it cannot be justified without circularity.
- Unity of consciousness
The way all of a person's experiences at one time seem to belong together in a single field, experienced by one subject.
- Utilitarianism
The moral theory that the right action is the one that produces the greatest total wellbeing, counting everyone's equally.
Wikipedia · What makes an action right?, Do animals have moral rights?, The drowning child, The veil of ignorance
- Utility
A measure of how good an outcome is for someone, used in ethics and decision theory. It need not be the same as money or pleasure.
V
- Vagueness
The property of words like 'bald', 'heap' and 'tall' that have borderline cases and no obvious sharp boundary.
- Validity and soundness
An argument is valid if its conclusion must be true whenever its premises are true. It is sound if it is valid and its premises really are true.
- Veil of ignorance
Rawls' device for fairness: choosing the rules of society without knowing what position you would occupy in it.
- Verificationism
The view that a statement is meaningful only if it can be verified, at least in principle, by experience, or is true by definition.
- Virtue
A stable trait of character that makes someone good and helps them act and feel well, such as courage, honesty or kindness.
Wikipedia · What makes an action right?, Should you only care about what you control?, Would you be good if no one could see?
- Virtue ethics
The approach to ethics, rooted in Aristotle, that focuses on character and asks what a good person would do, rather than on rules or consequences.
W
- Wave function
The mathematical object in quantum mechanics that describes a system and gives the probabilities of the results of measuring it.
- Wellbeing
What makes a life go well for the person living it. The main theories are hedonism, desire-satisfaction theory and objective list theories.
- What matters
Parfit's phrase for whatever is actually important to us in caring about our own survival, which he argued is psychological continuity rather than identity itself.
Appears in Would you step into the teleporter?
- Whole brain emulation
The hypothetical copying of a particular brain's structure in enough detail to run it as software, reproducing its behaviour.
Z
- ZFC
Zermelo-Fraenkel set theory with the axiom of choice: the standard foundation of modern mathematics, which avoids Russell's paradox by restricting which sets can be formed.