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    This index is a work in progress.

    This is a glossary of key philosophical terms which you are expected to know for all of your A-level philosophy units, though they will be of particular use for epistemology and you are welcome to use this as a beginner’s guide to philosophical terminology even if you are not currently studying for an A-level. The content of this guide is based on the new AQA specification, which you can find here. If there are any other terms which you feel should be included here or if you would like me to clarify something, please let me know!
    The bits in spoilers are just interesting addenda, not content you need to know for A-level (don’t panic!).

    Assertions/claims and propositions

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    The terms “assertion” and “proposition” are sometimes used interchangeably in colloquial speech, but in philosophy, they are not to be conflated.
    • A proposition is a statement which is capable of being either true or false (i.e. of having a truth value). This says nothing about whether it is true or false in actuality, only that it is written in a form such that it could potentially be true or false. For example, “spiders have 8 legs” and “2 + 2 = 5” are propositions, but “ice cream is delicious” is not because expressions of taste cannot be true or false (however “you like ice cream” can, and so it does count as a proposition).
    • An assertion is a certain type of proposition: a statement which is proclaimed to be the case. There are two important differences between assertions and propositions; 1) assertions are acts of speech and 2) assertions are actual, concrete claims that something is true or false, rather than claims which can potentially be true or false. For something to be proclaimed to be true/untrue it must first be theoretically capable of being true/untrue, therefore all assertions are propositions, but not all propositions are assertions.

    Propositions in ethics:

    In ethics, the debate surrounding moral cognitivism/non-cognitivism concerns whether ethical statements can be considered propositions. Non-cognitivists argue that a statement such as “lying is wrong” or “income equality is just” can neither be true nor false; rather, it is an expression of social norms, personal preferences or something else which is not a feature of the world and hence cannot have a truth value. This has far-reaching consequences for how we think about morality; if moral utterances cannot be true or false, how can we know what is right and what is wrong?

    Conditionals, antecedents and consequents
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    • In logic and philosophy, a conditional is a sentence of the form “if […], then […]”, for example “if it is cold outside, [then] I shall wear a coat.” Symbolically, this relation can be represented using \Rightarrow, \rightarrow or \supset, so p \Rightarrow q means “if p, then q.”
    • The antecedent is the “if…” part of the conditional, while the consequent is the “then…” part. In other words, the consequent is the event which is to occur and the antecedent is the condition under which it would occur: I shall wear a coat under the condition that it is cold outside.
    • Other statements which are not written as conditionals can be paraphrased as conditionals, for example, “all lemons are sour” is equivalent to “if something is a lemon, then it is sour.”
    • A conditional is false if and only if it has both a true antecedent and a false consequent; if the antecedent is false, the conditional is trivially true.

    For people who like grammar:

    Rearranging the syntax of our example sentence as “I shall wear a coat if it is cold outside” shows very clearly that the consequent (blue) is a main clause and the antecedent (green) is a dependent clause. The former is called the apodosis and the latter is called the protasis; an apodosis is a main clause whose validity/truth depends on that of a dependent clause/protasis.

    Proofs with conditionals:

    One can prove or disprove a conditional by making assumptions about certain parts of it. The most obvious way is to assume that the antecedent is true and then prove that the consequent is true using that assumption, which shows that the consequent is true if the antecedent is true, but you could also do this “backwards” by assuming that the consequent is false and proving that the antecedent is false. This is called a proof by contrapositive. Another approach is a proof by contradiction, which you might know of from maths; in logic, this involves assuming that the conditional is false (i.e. that the antecedent is true and the consequent is false) and using that assumption to reach a contradiction, thereby showing that the assumption is false and the conditional is true.

    Analytic vs. synthetic truth

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    This concept is going to come in very useful when you study the empiricism/rationalism debate, and most other epistemological questions.
    • An analytic truth is true by definition, and denying it would therefore be contradictory. For instance, if one were to say “this circle is not round”, it would be immediately obvious that this is a contradiction because "roundness" is inherently part of the definition of a circle, hence it is analytically true that circles are round. I like to think of analytic truths as “self-contained” truths: all the components needed to prove that an analytically true statement is the case are contained within the statement itself.
    • In contrast, a synthetic truth is not self-contained because its truth relies on a feature of the world rather than on the definitions of the words involved. The definition of “the sky” does not include the characteristic of being blue, so “the sky is blue” is a synthetic truth; we know that it is true through observation, rather than by definition.

    A priori vs. a posteriori
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    This is another really important epistemological distinction for when you study empiricism and rationalism.
    • A priori is a Latin term literally meaning “from the first [thing].” The “first thing” in question is the mind, hence a priori knowledge is knowledge gained by theoretical means (through logical reasoning, or the analytic truth of the known statement) or gained independently of experience.
    • A posteriori means “from what comes after”, “what comes after” being “experience.” If something is known a posteriori, it is known through experience, or known “empirically.”
    • These terms do not have to be used in an epistemological context; “a priori” can refer to theoretical concepts in general. “A posteriori” is used less often outside epistemology because “empirical” is more common as a general adjective.
    • Empiricists hold that all knowledge ultimately originates in experience, so they believe that we cannot have a priori knowledge, or when we can, it amounts to knowledge of what is analytically true. This means that, according to empiricists, a proposition whose truth value can be known a priori (such as “4 is an even number”, which is also arguably analytically true due to how even numbers are defined) is not substantive since it would be true regardless of how the physical world is and human experience has no bearing on it.

    Kant and synthetic a priori knowledge:

    Kant rejected this empiricist idea that a priori knowledge is necessarily analytic and not substantive. He argued that innate knowledge of theoretical concepts (a common example is causation, or the relation between cause and effect) is needed to learn in order to learn about the existence of the concept in reality through experience. Theoretical ideas which are known innately but which can also be experienced and applied in the physical world, such as the idea of causation, are known in the Kantian lexicon as synthetic a priori knowledge. Another example of synthetic a priori knowledge, according to Kant, is mathematical statements; arguably, the truth value of a mathematical proposition is not necessarily immediately evident given the definitions of the components of the statement.

    Necessary vs. contingent

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    • A necessary truth is true in all possible worlds; it is impossible for its negation (opposite) ever to be true, regardless of the state of the world. This is, in general, because it is an a priori truth whose negation is logically impossible, however some necessary truths can relate to physical objects rather than to the abstract logical concepts which must always be true. For example, water is always H20.
    • A contingent truth is, as the name suggests, dependent on the surrounding world and circumstances; it is logically possible for it to be false.

    Inductive vs. deductive argument
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    • The general rule to remember is that deductive arguments go from the general to the specific, whereas inductive arguments go from the specific to the general.
    • By making a deductive argument, one is trying to argue that if the premises of an argument are true, the conclusion cannot be anything other than true. A deductive argument which accomplishes this is valid; a deductive argument which accomplishes this and has justified, actually true premises is sound. All deductive reasoning is either valid or invalid (there is no "semi-valid". An example would be something like:

    P1) It is raining all over London.
    P2) Enfield is in London.
    C) It is raining in Enfield.
    • The above format of presenting an argument is called a syllogism (P means premise and C means conclusion).
    • In contrast, the strength of an inductive argument is continuous. A strong inductive argument shows that the conclusion is likely, rather than certain, to be true, so an inductive argument can have levels of strength (not validity, since the purpose of the argument is not to show that a conclusion is definitely true). For example, "it is raining in Enfield, therefore it is raining all over London."
    • New evidence can affect the strength of an inductive argument; if Enfield generally had different weather to the rest of London, the above argument would be weaker.

    More coming soon!

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