Epistemology — Key Terms and Definitions

Knowledge, Justified True Belief and Gettier

Epistemology: The area of philosophy that examines the sources, limits and nature of our concepts and knowledge.
Concept: A constituent of a thought/proposition.
A priori knowledge: Propositional knowledge not acquired from/not justified by experience.
A posteriori knowledge: Propositional knowledge acquired from/justified by experience.
A priori argument: An argument in which all of the premises are a priori.
A posteriori argument: An argument in which at least one premise is a posteriori.
Analytic truth: A proposition whose truth depends only upon the meanings of its constituent terms/concepts. (For example, vixens are female foxes.)
Synthetic truth: A proposition whose truth depends upon how reality is in addition to the meanings of its constituent concepts.
Necessary truth: A proposition that is true in all possible worlds (i.e. it could not have been false).
Contingent truth: A proposition that is true in the actual world but false in at least one possible world (i.e. it could have been false).
Hume's Fork: The division of knowledge into only two types: (a) 'matters of fact' (a posteriori, contingent, synthetic) and (b) 'relations of ideas' (a priori, necessary, analytic).
Propositional knowledge: Knowing that a proposition is true/knowing that p (where p is a proposition). For example, knowing that it is raining.
Acquaintance knowledge: Knowing X (a place/thing/person) by [direct] contact (normally through experience) with X. For example, knowing the taste of pineapple/how pineapple tastes.
Ability knowledge: Knowing how to perform/complete a task/action. (For example, knowing how to swim.)
Individually necessary condition (for knowledge): A condition that is 'needed' for X. A necessary condition for X is one that must be fulfilled in order for something to be X(/knowledge). For example, a necessary condition for being a vixen is being a fox — something must be a fox in order to be a vixen.
Jointly sufficient conditions (for knowledge): Conditions that, together, are 'enough' for X (so that no more conditions are needed). Jointly sufficient conditions for X(/knowledge) are conditions that, when all fulfilled, guarantee that something is X. For example, being a fox and being female are, together, jointly sufficient conditions for something being a vixen.
Tripartite view of knowledge: The view that S knows that p if and only if: (1) p is true, (2) S believes that p and (3) S is justified in believing that p.
Lemma: A proposition that is used by someone as part of their justification of another proposition.
Gettier's counter-examples: Gettier's two counter-examples which aim to show that the conditions of the tripartite view are not jointly sufficient. They are cases where (1) Smith is justified in believing that p, (2) p is true and (3) Smith believes that p, but (4) (intuitively) Smith does not know that p. (NB: Other such examples are often called 'Gettier-cases' but the specification refers to his original two cases.)
Post-Gettier analyses/definitions of knowledge: Alternatives to the tripartite view in which Smith (in Gettier's counter-examples) would fail to meet at least one condition thus explaining his lack of knowledge.
Infallibilism (response to Gettier's counter-examples): The view that S knows that p if and only if: (1) p is true, (2) S believes that p and (3) S has a justification that guarantees the truth of p (S couldn't possibly be mistaken that p).
No false lemmas theory (response to Gettier's counter-examples): The view that S knows that p if and only if: (1) p is true, (2) S believes that p, (3) S is justified in believing that p and (4) S's belief that p is not inferred from any false proposition (i.e. S's justification for p does not include any false propositions).
Reliabilism (response to Gettier's counter-examples): The view that S knows that p if and only if: (1) p is true, (2) S believes that p, (3) S's belief that p was caused by a reliable cognitive process.
Epistemic virtue (an account of) / virtue epistemology (VTB) (response to Gettier's counter-examples): The view that S knows that p if and only if: (1) p is true, (2) S believes that p, and (3) S arrives at the truth of p due to the use of their epistemological virtues.

Perception as a Source of Knowledge

Perception as a source of knowledge: Perception is the process by which we (attempt to) gain knowledge about our environment (e.g. using sight) or our own body (e.g. using proprioception). It is distinguished from other possible sources of knowledge: introspection, memory, reason, and testimony.
Object: A (physical/mental) thing that has properties.
Ordinary objects: The everyday objects we are talking about when we talk about, say, chairs, footballs, spoons etc.
Mind-independent object: An object whose existence is not dependent on the existence of any mind/s.
Mind-dependent object: An object whose existence is dependent upon the existence of at least one mind.
Immediate object of perception: The object that a perceiver is directly aware of during perception.
Illusion: An experience where it seems to you as if there is a property/relation but the mind-independent object (which you are supposedly perceiving) does not have this property/relation. For example, when a straw is placed in a glass of water, there can seem to be 'bentness', but the mind-independent stick is straight.
Hallucination: An experience which is subjectively indistinguishable from an experience of a mind-independent object, but where there is no suitable mind-independent object (i.e. no mind-independent object that bears the right kind of relationship to your experience). For example, Macbeth has an experience that he takes to be of a dagger, but there is no mind-independent dagger.
Perceptual variation: The fact that a perceiver's experiences change along with changes in the perceiver's spatial position relative to the object (e.g. angle of view) and/or the physiology of the perceiver (e.g. colour-blindness). This means that it seems as if there is a change in properties, but the mind-independent object's properties are not changing. For example, as I walk towards an object there will be changes to my experience in terms of shape and size, but the object does not change shape or size.
Time-lag: The fact that the physical processes associated with experience (e.g. the visual process) take a finite amount of time (the 'time-lag'), no matter how small. This means that at the exact moment that it seems to you as if there is an object with particular properties, it could be the case that the way things are in the external world at that moment are different to how they seem at that moment to you. For example, when it seems to me that there is a star in the night sky, it could be the case (and sometimes is the case) that the star has exploded by that point.
Direct realism: The view that the immediate objects of perception are mind-independent objects and their properties. (This involves (a) realism — the view that mind-independent material/physical objects and their properties exist — and (b) directness — the view that we perceive these mind-independent objects immediately.)
Quality (Locke): A 'power [of an external mind-independent object] to produce an idea in our mind'.
Primary quality (Locke): A power of mind-independent objects to cause an idea in our minds that resembles the actual inherent properties of the object. The primary qualities are number, extension, motion, shape, solidity. They are inseparable from the object; the object cannot be conceived of as not having them; they do not vary based on the perceiver; they can be accessed by more than one sense.
Secondary quality (Locke): A power of a mind-independent object to cause an idea in our minds that does not resemble the actual inherent properties of the object. The secondary qualities of a mind-independent object are colour, taste, smell, sound, (felt) texture. The object can be conceived of as not having them; they vary based on the perceiver; they cannot be accessed by more than one sense.
Sense-data: Sense-data are what we are directly/immediately aware of during perception. They have the properties that they appear to have; properties that are known to us with certainty (maybe infallibly). They are private (only experienced by one perceiver). According to indirect realists they are mind-dependent objects caused by, and mediating our experience of, mind-independent physical objects.
Indirect realism: The view that the immediate objects of perception are mind-dependent objects (sense-data) that are caused by and represent mind-independent objects. (This involves (a) realism — the view that mind-independent material/physical objects and their properties exist — and (b) indirectness — the view that we perceive these mind-independent objects indirectly.)
Involuntary nature of our experience (Locke): The fact that our perceptual experiences are not under our control. Used as a reason for thinking that there is an external world that best explains this involuntariness.
Coherence of various kinds of experience (Locke and Cockburn): The fact that perceptual experiences from the different senses contain the same/similar information (coherence as corroboration — Locke) or, at least, change in reliable/regular/predictable ways (coherence as covariation — Cockburn). Used as a reason for thinking that there is an external world that best explains this coherence.
Berkeley's idealism: The (immaterialist) view that the immediate objects of perception (i.e. ordinary objects such as tables, chairs, etc) are mind-dependent objects (caused by God). All that exists is minds and their ideas.
The likeness principle (Berkeley) (mind-dependent ideas cannot be like mind-independent objects): The view that an idea cannot resemble anything other than an idea; that something sensible cannot resemble something insensible. Used to question the possibility of the representation involved in indirect realism.
The 'Master' argument (Berkeley): Berkeley's argument that we cannot conceive of mind-independent objects since to conceive of them requires them to be in the mind, and therefore to be mind-dependent.
Solipsism: The view that my mind is all I can have knowledge of (epistemological solipsism). The view that only my mind exists (metaphysical solipsism).
Scepticism about the existence of mind-independent objects: The view that we do not/cannot know that mind-independent objects exist. Also known as external world scepticism.
External world: The sum total of all mind-independent objects and their properties. The world external to our mind/s.

Reason as a Source of Knowledge

Reason as a source of knowledge: A priori methods of gaining knowledge/concepts: innate knowledge/concepts, knowledge from intuition and deduction, analytic truths/'relations of ideas'.
Empiricism: The view that (a) all of our concepts are ultimately caused by experience; there are no innate concepts (concept empiricism) and (b) all synthetic knowledge is a posteriori (the justification is dependent on experience); there is no innate knowledge and no synthetic a priori knowledge.
Simple concept/idea (Locke/Hume): A concept which (a) cannot be analysed in terms of any other concepts (it is phenomenally simple/'uncompounded') and (b) only exists as the direct effect of an experience (for Hume, as a 'copy' of a simple impression).
Complex concept/idea: A concept which (a) can be analysed in terms of other, ultimately simple, concepts and (b) need not be the direct effect of experiences.
Impressions (Hume): Hume's term for experiences (which for him includes sensations, perceptions, emotions). They are/seem more 'forceful and vivid' than ideas/concepts.
Ideas (Hume): 'Idea' is Hume's term for a concept and includes simple and complex ideas/concepts. They are caused by impressions, are 'copies of impressions' that we can recall and they are/seem less 'forceful and vivid' than impressions.
Innatism: The view that some rationalists take that (a) our mind has always contained particular truths and/or concepts which (b) we can 'discover'/'uncover'/'recollect' and which (c) are not/could not be from experience. They are a priori, though experience might have some role in 'triggering' our discovery of them. The mind is, therefore, not a 'tabula rasa' as empiricists suggest.
Tabula rasa: 'Tabula rasa' means 'blank slate' and this refers to the empiricist view that no concepts or truths exist within the mind at the moment that it begins to exist. It is, therefore, the denial of innatism.
'Slave boy' argument (for innatism) (Plato): Plato's argument that geometric truths must be innate, since an uneducated slave boy can come to recognise one such truth (a version of Pythagoras' theorem) without having been taught it and only by being asked questions.
Leibniz's argument (for innatism) based on necessary truths: Leibniz's argument that necessary universal truths must be innate, since no amount of experience of contingent truths about particulars can justify them (e.g. that all triangles have three sides).
A priori intuition: A belief which is (1) non-inferentially justified (you do not infer an intuition from something else that you believe) and (2) a priori/'rational' (i.e. justified without the need for experience/s). For Descartes, the cogito (I am, I exist) is an example of an a priori intuition.
Intuition (Descartes): A belief which is (1) non-inferentially justified (you do not infer an intuition from something else that you believe) and (for Descartes) (2) a priori/'rational' (i.e. justified without the need for experience/s). For Descartes, the cogito (I am, I exist) is an example of an a priori intuition.
Deduction (Descartes): By 'deduction' Descartes meant an argument that is (a) deductive and (b) a priori.
Intuition and deduction thesis (Descartes): The view that all knowledge is either: (a) justified non-inferentially by a priori intuition or (b) justified inferentially through a priori deduction (ultimately based on a priori intuitions). Using these methods, according to Descartes, we can (re)gain knowledge of self (including the nature of our minds), God and the external world.
Clear and distinct idea (Descartes): A concept/belief for which (a) its content/truth is obvious to an attentive mind (it is clear) and (b) any concepts/beliefs not belonging to it are excluded from it (it is distinct).

Scepticism

God: A perfect being that (traditionally) has the following attributes: omniscient, omnipotent, omnibenevolent, and is either eternal/timeless or everlasting.
Cogito (Descartes): One's knowledge of one's own existence — 'I am, I exist'. An a priori intuition which (according to Descartes) is the foundation of one's other knowledge and is undoubtable (it survives sceptical doubt/arguments).
Descartes' sceptical arguments / 'waves of doubt': The arguments that Descartes uses as part of his method of doubt: (1) the 'illusion' argument — illusions show that we cannot trust our experiences (at least in terms of near/large objects); (2) the 'dreaming' argument/hypothesis — it is impossible to rule out the hypothesis that I am dreaming now; and (3) the 'evil deceiver/demon' argument/hypothesis — it is impossible to rule out the hypothesis that an evil being has complete control of my thoughts and experiences.
Normal incredulity: Doubt that arises about a specific claim because of beliefs you don't doubt and where the reasons for this doubt can, in principle, be removed.
Philosophical scepticism: The view that we lack knowledge in such a way that the reasons for this doubt (arguably) cannot be removed.
Local scepticism: Philosophical scepticism about a specific domain (e.g. those about the past) and/or based on a specific type of justification (e.g. memory).
Global scepticism: Philosophical scepticism applied to all knowledge claims. The view that we have no (or next to no) knowledge; that (almost) none of our usual forms of justification for our beliefs are adequate.

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