The Origin Of Thought

Introduction

The Principles Directing This Investigation

Chapter 1

The Two Principles Of Method In Philosophy

26. Our investigation must be directed by two principles.

First: 'When explaining facts about the human spirit, we must not take into account less than is necessary for the explanation.' The reason is clear: as long as we take into account less than is needed, it is impossible to posit a sufficient explanation of the facts. In a word, we have not explained them. Let us suppose, for example, that someone observes colour and sound sensations, two facts of human sensibility, and claims to explain them both by allowing human beings one sense only, either sight or hearing. In this case, the facts remain unexplained because their reduction to the single sense of sight cannot show how the eye hears, while their reduction to hearing alone cannot show how the ear sees.

27. Second: 'In our explanation of these facts, we must not take into account more than is required'(1). Non-essentials are superfluous to the explanation and, as entirely gratuitous, can be gratuitously denied. Two human senses, for example, may be posited to explain one kind of sensation. This is obviously ridiculous because two causes, one of them superfluous and without foundation, have been assigned to a single kind of fact.

28. Meditation on the human spirit must lead us, therefore: 1. to recognise and uphold everything necessary for explaining all characteristic facts obtainable through careful observation; 2. to accept only the minimum required to explain these facts. In other words: 'Of all the complete explanations of the facts about the human spirit, the simplest and that requiring the fewest suppositions is to be preferred.'

Notes

(1) It is easy to see that these two principles, taken together, are only the principle of sufficient reason divided into its parts.