A NEW ESSAY
concerning the
ORIGIN OF IDEAS

SECTION ONE

Chapter 1.

26. The two basic principles by which I wish to be guided in my argument are:
First: 'In explaining facts connected with the human spirit, we must not make fewer assumptions than are required to explain them.'
The reason for this is obvious: unless we assume all that is needed, we can never say that we have succeeded in putting forward a sufficient cause, that is, a reason explaining the facts. For example, anyone who observes colour and sound, two facts associated with the human senses, and claims to explain both by referring to hearing alone or sight alone, does not explain fully the nature of these two facts because, in reducing both to sight, he will never be able to understand how the ear perceives sounds. If, on the other hand, he reduces both to hearing, he will never be able to explain colour-sensation satisfactorily.

27. Second: 'We must not make more assumptions than are needed to explain facts.'(39)
Any assumption over and above what is required for such an explanation is superfluous and completely gratuitous. But any statement made gratuitously can be refuted and denied gratuitously. For example, if we were to take two senses and use them purely to explain a single species of sensation, we would be mocked for attributing two causes to a single kind of fact. One of the causes will obviously be superfluous and introduced unthinkingly.

28. Thus, in considering the nature of the human spirit, we must acknowledge and admit
1. everything needed to explain all the characteristic facts provided by careful, complete observation;
2. nothing more must be admitted. In other words, we must acknowledge and admit the minimum possible. 'Of all complete explanations of facts connected with the human spirit, we should opt for that which is simplest and requires fewer assumptions than other explanations.'

(39) It is easy to see that these two principles, taken together, are simply the component parts of the principle of sufficient reason.