But in very truth the child was born, and, as Bacon says, for forty years grew and developed, with many changes yet the same.

Bacon was most tenacious, not only of ideas, but even of the phrases, images, and turns of speech in which they had once flashed on him and taken shape in his mind.

The features of his undertaking remained the same from first to last, only expanded and enlarged as time went on and experience widened; his conviction that the knowledge of nature, and with it the power to command and to employ nature, were within the capacity of mankind and might be restored to them; the certainty that of this knowledge men had as yet acquired but the most insignificant part, and that all existing claims to philosophical truth were as idle and precarious as the guesses and traditions of the vulgar; his belief that no greater object could be aimed at than to sweep away once and for ever all this sham knowledge and all that supported it, and to lay an entirely new and clear foundation to build on for the future; his assurance that, as it was easy to point out with fatal and luminous certainty the rottenness and hollowness of all existing knowledge and philosophy, so it was equally easy to devise and practically apply new and natural methods of investigation and construction, which should replace it by knowledge of infallible truth and boundless fruitfulness.

His object--to gain the key to the interpretation of nature; his method--to gain it, not by the means common to all previous schools of philosophy, by untested reasonings and imposing and high-sounding generalisations, but by a series and scale of rigorously verified inductions, starting from the lowest facts of experience to discoveries which should prove and realise themselves by leading deductively to practical results--these, in one form or another, were the theme of his philosophical writings from the earliest sight of them that we gain.
He had disclosed what was in his mind in the letter to Lord Burghley, written when he was thirty-one (1590/91), in which he announced that he had "taken all knowledge for his province," to "purge it of 'frivolous disputations' and 'blind experiments,' and that whatever happened to him, he meant to be a 'true pioneer in the mine of truth.'" But the first public step in the opening of his great design was the publication in the autumn of 1605 of the _Advancement of Learning_, a careful and balanced report on the existing stock and deficiencies of human knowledge.

His endeavours, as he says in the _Advancement_ itself, are "but as an image in a cross-way, that may point out the way, but cannot go it." But from this image of his purpose, his thoughts greatly widened as time went on.