Sunday, 20 November 2011

Hume on Induction

Hi I have been catching up on Hume over the past two weeks. I have an exam in two weeks, just a single question to answer in 45 minutes. and then an essay to write before the 20th.  We have been told the types of questions in advance and I have chosen to do one the topic of Induction. Here is a short essay on the subject. I had known vaguely that Hume was the first person to think that there could be no rational justification for the principle of induction. On the other hand I had never realised just how powerful his arguments were. Here is a short OU TMA type essay on the subject which I wrote to clarify my ideas on the subject (although a bit short by TMA standards). I hope you find it interesting.

I will write an essay on Hume's Scepticism for the seen part of the assessment

Hume on Induction

This essay will summarise Hume’s arguments as to why there cannot be any rational argument or argument from experience (which Hume call’s probable or moral reasoning) to justify our use of Induction. Thus we can only justify our inductive reasonings by custom or habit. Given Hume’s empiricist views, that Hume thinks there can be no rational justification for induction is not so surprising. However it is quite surprising that according to Hume there can be no empirical justifications for induction either. The argument that follows is based on section 4 of Hume’s Enquiry (Hume, 1748 pp 20-29). Peter Millican (2002 ) has shown that the argument presented in the enquiry is quite different from that in the Treatise (Hume, 1739) and that Hume introduces a new premise in the argument of the Enquiry that is not present in the argument of the treatise, namely the appeal to the uniformity of nature. However as Hume points out this cannot be used to justify the principle of induction on appeal to experience as it involves circular reasoning. Neither can the uniformity of nature be justified on rational grounds (In what follows the numbers in square brackets refer to the relevant paragraph in section 4 of the Enquiry)
Induction, as Hume defines it [16], is based on a move from the fact that an object has in the past been associated with a particular effect to the fact that is reasonable to assume that similar objects will in the future be associated with similar effects. Note that Hume is not saying that from an observation of many white swans, all swans are white as traditional accounts of the problem of induction would have it. He only wants to make a move from previous observations of an object to the behaviour or properties of a similar object presented to us. The dilemma is that Hume cannot see a way to justify this principle apart from an appeal to custom or habit.
A simplified structure of Hume’s argument is as follows (For a more detailed analysis see Millican 2002 Ch 4)
Premise 1: (Hume’s Fork) All reasoning is either about relations between ideas or of matters of fact. [1]
Premise 2: Reasoning about relations between ideas are based on deductive or a priori reasoning.[1]
Premise 3: Reasoning about matters of fact are based on probable reasoning or experience. [2]
Premise 4: In order to extend our reasoning about matters of fact beyond our immediate sense experience or memory we must appeal to reasonings based on cause and effect. [4]
Premise 5: Induction attempts to move beyond our immediate sense experience or memory to predict what will happen in the future, thus if there is a justification for induction it can only be by an appeal to cause and effect. (This is implicit in Hume’s argument)
Premise 6: All reasonings concerning cause and effect cannot be based on deductive reasoning. Therefore (Intermediate conclusion): from Premises 1 and 3 reasonings based on cause and effect must involve an appeal to experience [7].
Premise 7: All reasoning based on cause and effect involves an appeal to the uniformity of nature. However the uniformity of nature cannot be justified by an appeal to experience as this presuspposes the very thing we wish to assume. Neither are there any rational grounds for this proposition [19].

Conclusion: The principle of Induction cannot be justified either by an appeal to deductive reasoning or an appeal to experience. Hence we can only appeal to custom or habit to justify our inductive reasonings.

It should be pointed out that Hume is not denying the usefulness of inductive reasoning. Indeed he appeals to it in the latter half ot the Enquiry he just wants to alert people that it is impossible to justify this principle apart from an appeal to custom or habit.In what follows I will expand on the basic structure given above.

Hume begins section IV by introducing what has been labelled as Hume’s fork namely that reasoning can be divided into two types That concerning relationships between ideas and that which can be divided into relationships between matters of fact. By the first Hume has in mind reasoning involving mathematical or geometrical truths. Thus a proof that the internal angles of a triangle add up to 1800 would be achieved by deductive reasoning from Euclid’s axioms. There are a number of important features of this type of reasoning

1) Once demonstrated a theorem achieved by deductive reasoning will always be true.

2) It is impossible to conceive of a contradiction, all triangles in Euclidean space have Internal angles adding up to 180 degrees.

3) It only takes one example of a proof by deductive reasoning to establish it as true for all cases.

On the other hand reasoning concerning matters of fact are not ascertained by deductive reasoning, but by what Hume calls probable reasoning. It is reasonable to assume that the sun will rise tomorrow, but it is possible to conceive that it will not rise without contradiction. Thus reasoning concerning matters of fact differ from those concerning relationships between ideas.

If we want to extend our knowledge regarding matters beyond immediate sense experience or memory we must make an appeal to cause and effect. If I’m asked why I know my friend is in France I will say because he told me or that I have a postcard which arrived from him this very morninng. The question thus arises, as to what is the type of reasoning concerning cause and effect. Hume argues that it cannot be by an appeal to deductive reasoning for the following reasons:

1) If a person is presented with a new object despite their having extemely good powers of reason he or she cannot, without appeal to experience predict any of its effects. Thus from the colour and consistency of claret, alone it is impossible to predict in advance its restorative or pleasurable effects.

2) It is perfectly possible to imagine a number of possibilities in any given situation without prior experience. Thus to use one of Hume’s favourite examples, when considering the collision of two billiard balls without prior experience it is quite possible to conceieve that one will avoid the other or that the first one will stop whilst the second one moves. However deductive reasoning based on say a knowledge of what Hume calls an objects secret powers will only be able to deduce one possibility.

3) Relationships of cause and effect require many observations to establish the relationship whereas deductive reasoning only requires one demonstration to establish the truth for all time.
Thus given the logic of Hume’s fork, relationships based on cause and effect can only be based on Experience [14].

This raises the key dilemma for Hume, because if we now ask what is the foundation of all our arguments from experience we are faced with a more difficullt question. Hume [15] claims that he can find no reason either from deductive or probable arguments. Hume argues that when we see for example, a glass of claret, without much knowledge of it’s ‘secret powers’ we immediately, based on our previous experience expect it to give us pleasure, but if drunk to excess will make us drunk and give us a hangover in the morning. Our reasonings for this and similar examples are based on an appeal to the uniformity of nature. However if we were to further ask what is the justification for this assumption, we can only appeal to experience. Thus the argument would be circular. It is expected that an object with a similar appearance to one we have previously encountered will behave in a similar manner, by appealing to the uniformity of nature, but our only foundation for this belief is based solely on our previous experience.

Again it is not possible to justify the uniformity of nature on deductive grounds, because we know that in practice whilst similar objects have similar effects they are never quite the same. ‘Nothing so like as eggs’ [20] as Hume points out, but each egg we taste will taste slightly different. On the other hand whenever a proof of deductive reasoning occurs it will be true once and for all. Thus if it were possible to deduce the properties of eggs in a purely rational manner, it would apply to all eggs without fail and there would be no variation between them. Furthernore it takes experience of a number of eggs to deduce their properties whereas a theorem produced by deductive reasoning only requires one demonstration to prove it for all time. As a final point it is quite possible to conceive that the laws of nature might change or that they would be different to what they are now, but this contradicts the feature of deductive reasoning that it cannot allow of any contradictions.

Thus there is a real dilemma, Hume has shown that inductive reasoning only works by an appeal to the uniformity of nature, on the other hand this principle cannot be justifed by an appeal to experience as this would involve us in circular reasoning. Neither can an appeal to deductive reasoning help to justify this principle. Thus there can be no form of reasoning either deductive or probable which will enable us to justify our inductive experiences. It would seem that we can only appeal to custom or habit.
Hume D 1739 ‘Treatise of Human Nature ‘
Hume D (1748) ‘An Enquiry concerning Human Understanding’ (Oxford Classics edition edited by Peter Millican Oxford 2007)
Millican P ‘Humes Sceptical doubts concerning Induction’ Ch 4 of Reading Hume on Human Understanding Oxford 2002.

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