Hume is the founder of irrational philosophy.

In the 17th century there were two groups of philosophies: the rationalists and the empiricists.

The rationalists said that the senses were unreliable. Knowledge could be acquired by introspection, by looking at your innate ideas and drawing conclusions from them. There was no need to look at the world and drawing conclusions from sense data.

The rationalists (Descartes, Spinoza, Leibniz) contradicted each other as none had contact with reality. They tended to become mystics.

The empiricists believed in sense data. Man has no innate ideas. All knowledge must be based on sense data, as Aristotle said: But the empiricists rejected Aristotle and became skeptics.

David Hume was an empiricist who then became a complete skeptic. He said you cannot know anything at all.

Skepticism was the result of empiricism.


How did that happen?

The empiricists rejected the theory of universals and offered their own belief which they called nominalism.


What are universals?

A universal is the common quality which each member of a class has. Universals are the basis for concepts. The nominalists say that there are no universals.

Think of the concept ‘dog’. When we leave out all qualities that vary from dog to dog, then what is left is a universal. But the nominalists say they find nothing left to concentrate on. Concepts are arbitrary, though convenient. Nominalists believe we have only one, not two cognitive faculties. The two faculties which man has are sense perception and reason. The nominalists deny that we have reason.

The thoughts and ideas we have are images of objects. So for a nominalist, sense perception alone is the means of knowledge. Reason is out. This theory is known as sensualism.

Empiricists who are nominalists are also sensualism. Sensualism leads to skepticism. You cannot know anything by drawing conclusions from sense data with the help of reason.

The sensualists say that a word is meaningful only if you can perceive the object that it stands for. If not, the word is meaningless. Words cannot stand for concepts, since there are no concepts, they say. Hume said all conceptual knowledge is meaningless. Here is how he was forced to follow skepticism.

Hume takes any concept and asks if you can perceive it directly with your sense organs or at least form an image of it. If you can’t, Hume says it is meaningless. In this way Hume destroys all concepts.

Take, for example, the concept of causality. Suppose you throw a stone through a window, and the glass in the window breaks. There are two events: one, the stone hits the window and two, the glass breaks. But does that mean one event causes another? Causality has three elements, says Hume.

First, the two events must be directly connected in space. In this case the stone is connected spatially with the window. That’s fine.

Second, the two events must be connected in time. The glass breaks as soon as the stone hits it. Fine, so far.

Third, there must be a necessary connection between the two events. Now the trouble starts.

Hume asks you if you can perceive necessary connection. No. Then the third condition of causality is not fulfilled.

Therefore, says Hume, causality is non-existent.


People believe in causality however. Why?

The reason is that in the past we saw a stone hitting the window and the broken glass together. So we associate the two events causally and conclude falsely that the glass will break when the stone hits it in the future, says Hume. He says, what happened in the past does not prove it will happen in the future. What happened in the past was only coincidence.

A round ball rolled on the ground when you threw it on the ground. But that was in the past. The next time you throw the ball, it might turn into a stick or cube or a book.

Can you generalize and predict the future, tides or eclipse? No, says Hume. You can’t assume the future will be like the past. The tides and eclipses need not take place at all.

So nominalism leads to sensualism. Sensualism attacks all concepts like „necessity“. Thus causality, which depends on necessity as a factor, is attacked and destroyed.

Hume says there is no logic in our world. Anything can happen. All events are separate and not causally connected, or explicable. All events are unreliable. No fact necessitates another fact. All our experiences are non-rational.

Hume came to the strange conclusion that there are no entities, just like Heraclitus said. How?

Every entity such as a table has a number of qualities which are necessarily connected with one another, such as size, shape, weight, texture, color, etc. These qualities cannot exist separately. Why not, says Hume. There is no necessity for them to remain together. They can separate and so we have no entity but only qualities existing spatially apart.

So in Hume’s metaphysics there is a Heraclitean flux of sense data and separate qualities, no entities. There are no causal connections between events. This is the world of sensualist Hume who says man has no conceptual faculty. Anything can happen.

All truths however are not unreliable. Hume says there are truths that are necessary but they tell you nothing about reality.

Hume uses the word „necessary“ although he says that that word is meaningless.

Hume uses concepts in his philosophy. Of course that is wrong. If you attack concepts, you shouldn’t use them. Hume admits that it is impossible to live by his philosophy. It is impractical. He would visit his friends, forget his philosophy and live in a world of entities and reality and causality. Then he would go home to his books and find them absurd.

Hume is the founder of irrational philosophy. He said you should lead your life by non-rational instinct, like animals.

But let’s get back to necessary truths. Hume says there are two types of truth:

  1. analytic truths; and
  2. synthetic truths.

Synthetic truths are empirical. They depend on experience: There are skyscrapers in the city; the trees are big, etc. You cannot discover these truths by logic. You can imagine their opposite, e.g. there are no skyscrapers in the city.

Synthetic truths depend on experience, i.e. they are a posteriori. You can’t get knowledge of necessity, causality, freedom, etc. from experience.

Analytic truths are necessary truths, e.g. ‘triangles have three sides’.

These truths are the result of our arbitrary use of definitions. Whatever depends on definitions are analytic or a priori truths.

So you have a dilemma here.

If something is analytic, it has nothing to do with reality. If you can prove it, it is analytic.

If you can’t prove it, it is synthetic, and you can’t tell if it will be true the next minute.

All this leads you naturally to total skepticism. All you do is watch the sense experiences passing by. Everything is unintelligible. You can’t make sense of anything in this world. Man has no conceptual faculty. He lives on the perceptual level like any animal. There are no entities. There is no causal connection between events. Necessary, analytic truths are just arbitrary conventions.

What to do? This is the problem Hume left and Kant tries bravely to save the world from this situation. Even skeptics live in reality and they can live only with a knowledge of reality. But if you reject this knowledge, how can you live? Skeptics were upset by their own conclusions. Without knowledge of reality, they were helpless. Both mysticism and skepticism are useless.

All philosophers said that it was important to know reality. Their ideas of reality were different, but they believed in reason and were dissatisfied with skepticism.

But Kant said we don’t need reality. It is not necessary to be skeptical. We don’t know reality, but it is not important that we do not know reality.

Even today people say nobody knows what reality is, what is true, what is right, what is wrong, what is false. If you say your thoughts don’t correspond to reality, Kant says reality is dispensable.

Why did he say that? Kant wanted to solve Hume’s problem.

What was Hume’s problem?
He was completely frightened and confused in this world.

What sort of world is this world? Hume says this is a world without objects.