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All human activity, and in particular, investigation of nature, presupposes that our experience is not misleading - that it is typical, that it is a fair sample of the general behaviour of nature.
Particular examples of induction
and abduction are unified by certain general methods. These are:
Mg: 'Patterns in experienced events also exist in unexperienced events, until you have evidence to the contrary.
Mp: 'True theories make experienced events as high-chance as possible '.
These two methods can also be expressed as the theory or presupposition Tp: "Our available evidence is a fair sample; it is not fixed or biassed so as to be misleading. If we generalise from our experience, we will always go less wrong than if we just guess. We can use our experience as a guide to unexperienced events."
This most general presupposition - that our experience is not misleading - is the fundamental presupposition; from it derives the possibility that we can benefit from our experience. With this presupposition, the possibility arises that we can use our limited experience to form generalisations about nature as a whole, about the future and about the past, and about situations that we have not experienced. Without it, we would be limited to truths about our immediate experience, and recollection of such experience.
Scepticism concerning the method of simple induction has a long history. David Hume defends the view that since we only experience particular associations of one atomic event with another (experience of flames and burning), not necessary connections, we have no justification in believing that the next flame will burn us, nor that these things are necessarily connected. We have no justification in forming the universal generalisation that, as a matter of fact, all flames will burn us - that all things with the property of being flames will also have the property of burning us; we have no justification, furthermore, in forming the conjecture that these properties are necessarily connected.
Attempts to defeat this scepticism are legion. Whether any succeed is not at issue. All that matters for our present purpose is that these presuppositions are indeed made - justified or not.