Knowledge empiricism Michael Lacewing

Analytic and synthetic propositions An analytic proposition is true or false in virtue of the meanings of the words –Squares have four sides –Not all analytic propositions are obvious: in five days’ time, it will have been a week since the day which was tomorrow three days ago. A synthetic proposition is one that is not analytic, i.e. it is true not in virtue of the meanings of the words, but in virtue of the way the world is –Many ripe tomatoes are red.

A priori knowledge A posteriori: knowledge that requires (sense) experience to be known to be true –Snow is white. A priori: knowledge that does not require (sense) experience to be known to be true –Bachelors are unmarried. The distinction is not about how we come to understand a claim, but how we can establish whether it is true or not.

Rationalism v. empiricism Is all a priori knowledge knowledge of analytic propositions? Are all synthetic propositions known a posteriori? –Empiricism: yes –Rationalism: no Empiricism: if a proposition is not made true through logic or meaning, then it can only be established by sense experience. Rationalism: we can have a priori knowledge of synthetic propositions –E.g. through reason or innately.

A refinement The debate only applies to knowledge of the world outside one’s mind –There are many synthetic propositions about one’s mind that are known not by ‘sense experience’ but introspection or reflection.

Hume’s ‘fork’ We can only have knowledge of –Relations of ideas –Matters of fact. Relations of ideas: –‘Can be discovered purely by thinking, with no need to attend to anything that actually exists anywhere in the universe’ –Are intuitively or demonstratively certain (known by deduction) –It is a contradiction to deny them.

Matters of fact ‘Propositions about what exists and what is the case’ Known through sense experience – current or by memory – and induction. Whatever goes beyond experience rests on causal inference. Knowledge of causes and effects is gained through repeated experience –You cannot work out through a priori reasoning what causes or effects something will have.

Empiricism on knowledge For any field of enquiry, either –Knowledge is possible, but empirical, not a priori –Knowledge is possible and a priori, but analytic –Knowledge is not possible. Objection: this has a tendency to lead to scepticism.

Knowledge of physical objects (According to empiricism) all knowledge of synthetic propositions is a posteriori. ‘Physical objects exist’ is a synthetic proposition. But we cannot know, through sense experience, that physical objects exist. Therefore, (according to empiricism) we cannot know that physical objects exist. Therefore, either we cannot know that physical objects exist or empiricism is wrong. But we can know that physical objects exist. Therefore, empiricism is wrong.

Descartes, Meditation I We can be deceived by our senses. There are ‘no certain indications by which we may clearly distinguish wakefulness from sleep’.

Descartes, Meditations I But the elements of what I dream of must be ‘real’, mustn’t they – ideas of body, numbers, time? But what if all my experiences are produced in me by an evil demon who wants to deceive me? I can’t know, from sense experience, that this isn’t true. So I can’t know, from sense experience, whether physical objects exist.

Extending the objection If empiricism is correct, can we know whether God exists? –Is ‘God exists’ analytic? –If not, what sense experiences can establish whether God exists or not? If empiricism is correct, how can we have knowledge of morality? –Are moral claims analytic? –If not, what sense experiences give us knowledge of right and wrong? Many empiricists have denied that there is theological or moral knowledge.