A priori (prior to the evidence)

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Notes for A Priori, A Posteriori, and Synthetic A Priori Reading
You need beliefs in order to make sense of what you perceive.
How many of our beliefs can we base on reasoning rather than on evidence from perception?


A priori (prior to the evidence): knowledge we can have in advance of any empirical evidence
(note: all analytic beliefs are a priori)
e.g. “all bachelors are unmarried”

e.g. “all sisters are female”

e.g. “a moose cannot fit in my pocket”

e.g. “2 + 1 = 3”

  • They are a priori because knowing how to speak a language makes in unnecessary to consider evidence for them

As long as you understand the language and have definitions then it is not necessary to have evidence and it would be hard to doubt the belief as long as you understand what the words mean.

A posteriori (consider: post / posterior): knowledge that can be gained only after seeing the evidence
Kant (1724-1804): Synthetic a priori

  • Without some prior fixed beliefs we could not even begin to describe what we believe.

  • These beliefs are synthetic (i.e. manufactured). They are true not because of the way the world works, but because of the way our minds work.

  1. propositions of arithmetic and geometry

  2. belief that events have causes

  3. there are laws of nature that we can discover

  4. people and physical objects persist through time

    • We have to have some beliefs before we consider evidence. e.g. You can’t interpret what you see through a telescope if you don’t have some prior beliefs about distance in space.

Quine (1960s)

  • No fundamental difference between analytic and synthetic beliefs

  • No belief is true simply because of the meaning of words

  • All beliefs are true or false because of the way the world is and the meaning words have

  • Points out that the situation could change so it no longer makes sense to treat some of them as a priori

Web of Belief

  • Beliefs are linked in a vast network

  • Perceptual beliefs are near the edge and fairly easy to change

  • Beliefs near the centre and linked to other beliefs change very slowly as we get new evidence – they are insulated from evidence by the “beliefs” that surround it

Quine vs. Kant

  • Quine’s conclusion is that everyone must have some beliefs at the centre of their web of beliefs; these beliefs change with different people

  • No belief is safe: it might be reasonable to abandon what we believe

Both agree that for any person at any time the web will always have a centre.
Both agree that structured patterns of belief allow us to consider evidence, think, and explain the world around us.

Questions on Beliefs -- Answers

1. Which of the following are a priori beliefs, and which of the following are a posteriori?

* Vancouver is smaller than Montreal.

  • a posteriori: evidence required (observation; map; pop. figures)

* Four orcas and two humpbacks swimming together are six animals.

  • a priori: 4 + 2 = 6 can be reasoned; we know orcas & humpbacks are animals

* Ottawa is between Montreal and Vancouver.

* If Vancouver is west of Ottawa, and Montreal is east of Ottawa, then Montreal is east of Vancouver.

* Vancouver, Ottawa and Montreal are in Canada.

  • a posteriori: evidence required through experience

2. Kant came up with (what he thought) were some fixed beliefs common to all people. List three of them and come up with one of your own.

5. Which of the four statements below is/are a re-statement of Kant's views, and which is/are a re-statement of Quine?

  1. There are beliefs which at any time are at the centre of belief of any person.

    • KANT (beliefs are constant across time)

2. Given a person and a time, there must be beliefs which are not only at the centre of that person's beliefs but of any other person's too.

  • KANT (beliefs are constant across people)

3. Given a person and a time, there must be beliefs which are at the centre of that person's web of belief at that time.

  • KANT and QUINE (Quine, however, would say the beliefs vary by time; Kant would argue that these beliefs are constant)

4. There are beliefs which are at the centre of any person's web of belief at a given time, and given a different time or a different person there are beliefs which are at the centre of the web for that person and that time too.


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