Rhino looking for solid instructionA priori knowledge is knowledge that we can take for granted because it is established already by reason, maths or logic, as knowledge independent of observation or experience. We don’t have to reconfirm it. There’s no induction involved. We have decided already that the angles of triangles add up to 180 degrees (at least theoretically or absolutely in a flat-two-dimensional world) and that’s that. It’s a given in that it can be proved in itself without going into the outside world and checking it against triangles out there (which don’t really exist since they are a geometrical concept, so we couldn’t anyway). It is knowledge independent of experience. It is knowledge which is necessarily true, analytical knowledge.

Now it is true that we have to be taught this, so we have to experience this teaching and observe the (old-fashioned) teacher doing something with chalk and a blackboard but this is not what is meant by a priori knowledge. It’s the idea of a triangle and its properties which is a priori, not our learning processes which are irrelevant to this concept of the a priori.

Everything else (the phases of the moon, the workings of an air-conditioner, your girl-friend, gravity etc etc) which involves dependency (or contingency or being contingent) on measurement, observation, analysis of data, personal experience is a posteriori synthetic knowledge.


In an ultimate sense, everything is a posteriori but that is not a helpful conclusion. The distinction between a priori and a posteriori is a useful distinction if something like the above is accepted.


Immanuel Kant’s distinction. An analytic statement is one which does not add anything to what is already present in the concept.
All bachelors are unmarried men.
Schools are educational institutions.
The concepts of bachelors or schools are merely explained or expressed in another way.

Statements which add more to the concept, move away from what it is defined by, are synthetic.

Most bachelors in the United Kingdom will eventually get married.
Schools are often resented by their inmates.
The bits of information carried in these sentences are not contained within the concepts of
bachelors and schools. They are contingent, dependent on circumstances, not necessary or necessarily so, by processes of definition.
The distinction between the analytic and the synthetic has often been challenged or debated or redefined or regarded as dependent on metaphor or semantics or psychology (or even mathematical competence). Quine, for example, maintained that there is no such thing as a priori knowledge as all knowledge is potentially revisable in the light of new experience. Nonetheless, the distinction between the analytic and synthetic is really between explaining a concept and adding new information to it.

(prior to Kant, this might be regarded as a kind of contradiction)

Scepticism “the euthanasia of reason”.

Kant tries to show how metaphysics is possible.
Analytic truth – truth establishable by reason or definition before observation or experience, necessary truth.
Synthetic truth – truth which as to be established by observation; contingent truth, subject to problems like induction, subjectivity etc.
Analytic truths are a priori truth, truth before experience.
Synthetic truths are a posteriori, truth after observation or experience.

For metaphysics to be possible, Kant says there must be synthetic a priori truths (the crossover). If not, we can’t have metaphysics.

Kant’s revolution in epistemology places properties of the mind, not the properties of objects, at the centre of our understanding of the empirical world.

Both rationalists and empiricists talk of the world as impressing itself on the brain as a visual image of a rhino (for example) and on the mind or both as a proposition there’s a rhino out there. The mind is passively viewing nature.

Kant thinks the mind is active, not passive. The mind’s activity constitutes the world in its, the world’s, own terms, and we can only understand the world in these terms.

Space and time and causation are how we understand the world – the world has to be seen according to these forms of sensible intuition already located in our heads.
Kant uses the word forms to distinguish space and time themselves from our sensory experience of objects within space and time, something different.

The world we see is ordered in space and time because space and time are forms of our sensory experience. Sensory observation is not enough for Kant, it has to be disciplined by these forms ie shaped by our mental tendencies, into categories or forms of understanding to enable us to process sensory experience.

(According to Kant his categories or forms of understanding were twelve:- unity, plurality, totality, reality, negation, limitation, substance, causality, reciprocity, possibility, actuality, necessity – he arranged these in groups of three, somewhat over-tidily)

The transcendental deduction of the categories. We don’t look for confirmation for the categories in the world outside us because we are already looking at the world with those categories within our mental experience. Our inner subjective experience is possible only if there actually is an objective, empirical world outside us which conforms to the categories of the world (the modern scientist would argue that evolution has placed these forms or categories in our heads, or else we would not now be around at all but, helpless and confused, would have been eaten by a sabre-toothed cat or squashed by a mammoth).

Kant considers that this gives him synthetic a priori propositions which make metaphysics worthwhile.

Eg the concept of a cause, for example, can only be applied on the assumption that every event has a cause. We can only have the experience that we have, if every event has a cause.

Kant’s synthetic a priori can lead to subjective relativism, although he did not intend that.


The world we experience is a world of appearances, the phenomenal, ie how we see it. It is not totality of  the world as it is, the noumenal which we cannot experience by definition.

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