Antecedent / consequent

The antecedent and consequent are the two parts of a conditional statement, such as “if A then B”. In this example, A is the antecedent and B is the consequent.

  • Antecedent: The ‘if’ part of a conditional statement
    • E.g. “If Socrates is a man…”
  • Consequent: The ‘then’ part of a conditional statement
    • E.g. “…then Socrates is a mortal”

Valid / invalid

  • Valid argument: An argument where if the premises are true, the conclusion must also be true. For example:
    1. If Socrates is a man, then Socrates is a mortal
    2. Socrates is a man
    3. Therefore, Socrates is a mortal

Notice that if premises 1 and 2 above are true, it’s impossible for the conclusion (3) to be false. 

(Note: This is also a sound argument because it is valid and the premises are true.)

  • Invalid argument: An argument where it’s possible for the premises to be true but the conclusion be false. For example:
    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.

The reason it isn’t valid is because it’s possible for the premises to be true and the conclusion to be false. For example, Socrates may be the name of my cat – in which case premise 2 is still true – but the conclusion “Socrates is a man” would be false.

Deductive / inductive argument

Inductive and deductive are two different types of argument:

  • 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)
  • Inductive argument: An argument where the premises support the conclusion, but don’t logically guarantee it

(don’t get these confused with intuition and deduction, which is a slightly different thing)

Necessary / sufficient conditions

A correct definition of a concept will have conditions that are individually necessary and jointly sufficient.

  • Necessary condition: A condition that is necessary for something to be part of a concept, i.e. anything that does not have this condition will not be part of that concept
    • E.g. “unmarried” is a necessary condition of “bachelor” – you have to be unmarried to be a bachelor
  • Sufficient conditions: Conditions that, if all are met, are sufficient for something to be part of that concept
    • E.g. “unmarried” and “man” are sufficient conditions of “bachelor” – everything that is an unmarried man is a bachelor

(don’t get necessary conditions confused with necessary truths, which is a different thing)

Analytic / synthetic

Analytic and synthetic are two different kinds of truths.

  • Analytic truth: true in virtue of the meaning of the words
    • E.g. “A bachelor is an unmarried man” or “triangles have three sides” or “1+1=2”
  • Synthetic truth: true in virtue of how the world is
    • E.g. “Grass is green” or “water boils at 100°c”

Analytic truths cannot be denied without resulting in a logical contradiction. To say, “not all bachelors are unmarried”, for example, is to misunderstand the word bachelor – the concept of a married bachelor does not make sense. Similarly, one cannot coherently imagine a triangle with four sides because the very idea involves a contradiction.

Denial of a synthetic truth does not lead to a logical contradiction. For example, we can coherently imagine red grass in denial of the synthetic truth “grass is green”. Though experience tells us grass is not, in fact, red, there is no logical contradiction in this idea.

Necessary / contingent

The distinction between necessary and contingent truths is very similar to the distinction between analytic and synthetic truths:

  • Necessary truths must be true (so are more or less analytic truths)
    • E.g. “1+1=2” or “it is impossible for both a and not a to be true”
  • Contingent truths might not have been true (so are more or less synthetic truths)
    • E.g. “water boils at 100°c” or “Paris is the capital of France”

A priori / a posteriori

A priori and a posteriori are two different kinds of knowledge:

  • A priori knowledge: knowledge that can be acquired without experience of the external world, through thought alone
    • E.g. working out what 900 divided by 7 is
  • A posteriori knowledge: knowledge that can only be acquired from experience of the external world
    • E.g. doing an experiment to discover the temperature at which water boils

Rationalism / empiricism

The debate between rationalism and empiricism looks at whether we can acquire knowledge of synthetic truths using a priori reasoning (intuition and deduction):

  • Rationalism says there are some synthetic truths that can be learned a priori.
  • Empiricism says all knowledge of synthetic truths is acquired a posteriori.

Most a priori knowledge is knowledge of analytic truths and most a posteriori knowledge is knowledge of synthetic truths. The disagreement between rationalism and empiricism is whether this relationship holds in all cases, or whether there are exceptions. 

Descartes, for example, is a rationalist because he says we can learn synthetic truths such as “God exists” and “I exist” purely through intuition and deduction i.e. without empirical experience.

Intuition / deduction

Intuition and deduction are a priori methods for gaining knowledge:

  • (Rational) intuition: The ability to know something is true just by thinking about it
  • Deduction: A method of deriving true propositions from other true propositions (using reason)

Innatism / empiricism

The debate between innatism and empiricism asks whether humans have any innate knowledge, i.e. knowledge that they are born with.

  • Innatism says there is some knowledge that is innate knowledge.
  • Empiricism says there is no such thing as innate knowledge and that all knowledge is acquired after we are born.

Plato, for example, is an innatist and tries to show with his slave boy example that even without education, humans have knowledge of geometry.


Qualia are the subjective qualities of experience – i.e. what something feels like inside your mind. Qualia are not properties of objects, but properties of minds/experience. Examples of qualia include:

  • The redness I experience when I look at a ripe tomato
  • The taste of beer when I have a drink
  • The rough feeling when I run my hand over some sandpaper

Knowledge of qualia is sometimes called phenomenal knowledge – i.e. knowledge of what it is like to have a certain experience.

Interactionism / epiphenomenalism

Interactionism and epiphenomenalism are dualist explanations of how mental things and physical things interact.

  • Interactionist dualism says that the mental and physical can interact in both directions
    • E.g. Getting hit in my (physical) head causes my mental state of pain, and
    • my mental state of pain causes me to rub my (physical) head and say “ouch!”
  • Epiphenomenalist dualism says that the mental and physical only interact in one direction: From physical to mental
    • E.g. Getting hit in the (physical) head causes my mental state of pain, but
    • My mental state of pain don’t cause anything itself: It’s only the (physical) brain state that causes me to rub my (physical) head and say “ouch!” 


Supervenience is a relationship between two types of things. A supervenes on B if a change in B is needed before a change in A is possible. For example, molecular properties supervene on atomic properties.

This relationship is mostly relevant in metaphysics of mind: Property dualism says some mental properties (qualia) do not supervene on the physical because it’s possible for two things to be mentally identical but have different qualia. Physicalist theories, in contrast, say everything (including the mind/qualia) supervenes on the physical: If two things are physically identical, they will be mentally identical. 

Local / global scepticism

Scepticism is about doubting certain knowledge claims. We can distinguish between two different levels of scepticism:

  • Local/ordinary scepticism is when you doubt ordinary things in everyday life.
    • E.g. “I doubt whether he was the killer” or “I doubt that England are going to win the World Cup”
  • Global/philosophical scepticism is when you extend doubt beyond these normal levels and doubt pretty much everything that is possible to doubt.
    • E.g. “I might be dreaming, in which case I should doubt everything I am currently looking at” or “I might be a brain in a vat, so I can’t know for certain that today is Monday”

The classic global sceptic’s position is illustrated by Descartes in his 3 waves of doubt

In ordinary circumstances, for example, it doesn’t make sense to doubt whether you have hands (assuming you do and are looking at them). But if you’re in a philosophical setting, you can doubt you have hands because you can imagine scenarios where you would believe you have hands even when you didn’t. For example, you might actually just be a brain in a vat being stimulated by electricity to believe it has a body and hands etc. Or reality might be completely different and you actually have tentacles but an evil demon is deceiving you to believe you have hands instead. It doesn’t seem likely, but it’s philosophically possible.

Cognitivism / non-cognitivism

Cognitivism and non-cognitivism are two ways of classifying statements:

  • Cognitive statements aim to literally describe how the world is and are either true or false
    • E.g. “Water boils at 100°c” or “triangles have 3 sides” or “London is the capital of France”
  • Non-cognitive statements do not aim to describe how the world is and so are neither true or false
    • E.g. “ouch! or “Boo!” or “hooray!” or “don’t do that!” or “shut the door please”

The cognitivism/non-cognitivism distinction comes up in discussions of both moral language and religious language. There is a debate about whether moral language is cognitivist or non-cognitivist and there is a debate about whether religious language is cognitivist or non-cognitivist.


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.