XIX

In the process of exclusion are laid the foundations of true induction, which however is not completed till it arrives at an affirmative. Nor is the exclusive part itself at all complete, nor indeed can it possibly be so at first. For exclusion is evidently the rejection of simple natures; and if we do not yet possess sound and true notions of simple natures, how can the process of exclusion be made accurate? Now some of the above-mentioned notions (as that of the nature of the elements, of the nature of heavenly bodies, of rarity) are vague and ill defined. I, therefore, well knowing and nowise forgetting how great a work I am about (viz., that of rendering the human understanding a match for things and nature), do not rest satisfied with the precepts I have laid down, but proceed further to devise and supply more powerful aids for the use of the understanding; which I shall now subjoin. And assuredly in the interpretation of nature the mind should by all means be so prepared and disposed that while it rests and finds footing in due stages and degrees of certainty, it may remember withal (especially at the beginning) that what it has before it depends in great measure upon what remains behind.