Novum Organum, the new instrument, is Bacon's attempt to replace the old logic of Aristotle with a method fit for discovering nature. He writes in numbered aphorisms across two books, the first clearing away false ways of thinking and the second setting out his own procedure. His complaint is that the sciences of his day had stalled: they rearranged what was already known and won arguments, but produced few new works.
Bacon's starting claim is that human knowledge and human power meet in the same point. Where the cause of a thing is unknown, its effect cannot be produced, so nature is mastered only by submitting to how she actually works. The unassisted mind and hand are weak; both need helps and instruments, and the mind's instrument is a disciplined method rather than clever disputation.
The most famous part of the work is the doctrine of idols, the false notions that beset the understanding. The idols of the tribe are rooted in human nature itself, which reads its own order and feeling into things. The idols of the den are each person's private distortions of education, habit, and temperament. The idols of the market arise from words, which are formed loosely and force confusion upon thought. The idols of the theatre are the received systems of philosophy, which Bacon compares to stage plays presenting invented worlds.
Against these errors Bacon sets a contrast between two ways of reasoning. One, which he calls anticipation of nature, snatches at general conclusions from a few familiar instances and quickly satisfies the imagination. The other, the interpretation of nature, climbs gradually and regularly through experiment and particulars toward the principles most truly common in nature. The first is easy and persuasive; the second is laborious but sound.
The second book turns to that interpretation in practice, using the inquiry into heat as a model. Bacon gathers instances where a nature is present, absent, and varying in degree, then proceeds by rejection and exclusion: ruling out what cannot belong to the form before affirming what does. This patient, negative path, organized through orderly tables and ranked instances, is meant to yield laws that are solid and well defined, so that knowledge and operation grow together.