Popper, Karl ; Conjectures and Refutations - the growth of scientific knowledge (1968, c1963)
Popper begins to discuss Bacon's induction, mentioning his distinction between "anticipatio mentis" (attempts to "interpret what is manifest in nature in the light of non-manifest causes or of hypotheses"-Popper's words, 14) and "interpretatio naturae" (which Popper translates: "the (true) reading of nature"). The latter, Popper says, is "the spelling out of, the book of Nature" (me: basically, Nature is a book and we study its essential parts of God's language, the letters that it is composed of). "Interpretation" here is not meant to be subjective (all understandings of "interpretation" in the modern sense here should be avoided), but a simple reading of the objective text of nature. Popper says its original meaning was: "reading aloud for those who cannot read themselves". Today, a judge interpreting the law implies a certain latitude ; not so in Bacon's day: one applied it in the one and only right way. The latitude allowed is no more than that of a sworn interpreter translating a legal document (13, 14).
Popper further notes that for Bacon, his method of induction results in certain knowledge (episteme) and not in conjectures or hypotheses (me: What is manifest in nature can only be interpreted by that which is manifest). Regarding "anticipatio mentis" Popper quotes Locke: "men give themselves up to the first anticipation of their minds", which leads to guesswork and a misreading of the book of Nature (doxa). It is basically "prejudice" or "superstition" (related to 'anticipatio deorum", harboring naive or primitive or superstitious views about the gods). Evidently, Bacon himself (according to the Oxford English Dictionary) introduced the verb "to prejudge" ("to judge adversely in advance") in the English legal context.
Popper now states that what Bacon rejects, he accepts: a method of interpretation ; of conjecture, or hypothesis, that is. Bacon says that we must purge our minds of false beliefs, or idols, and this includes all anticipations, conjectures, guesses and prejudices - for these distort our observations (Nov. Org. i, 68, 69 end, 97) - our ability to discern "the kind of thing whose true essence or nature we wish to ascertain". For our souls "to face the eternal light of essences or natures" (Augustine, City of God, VIII, 3), "our impure prejudices must be exorcised by the invocation of counter-instances" (Nov. Org. ii, 16 ff). Then, we can begin to diligently spell out the open book of Nature, the manifest truth. Popper says that fundamentally, Aristotle, Bacon, Socrates (maieutic), and Descartes (systematic doubt) are all similar: destroying false prejudices in order to get at the "unshakable basis of self-evident truth" (14, 15).
Popper collapses their views into one by saying that the natural state of man is an "innocent eye which can see the truth", and state of ignorance due to the injury of the eye has to do with man's fall from grace, which can be partially healed by this purification. Therefore, this optimistic epistemology - "not only in Descartes' but also in Bacon's form" - "remains a religious doctrine in which the source of all knowledge is divine authority". He does note that "one might say that", "encouraged by the divine 'essences' or divine 'natures' of Plato, and by the traditional Greek opposition between the truthfulness of nature and the deceitfulness of man-made convention, Bacon substitutes, in his epistemology, 'Nature' for 'God'" - which may be why when our minds have been purified , even our sometimes unreliable senses (for Plato hopelessly impure) will be pure (15).
My summary: Socrates, Aristotle, Bacon and Descarte all believed that one could determine essences, and arrive at "the unshakable basis of self-evident truth". This is a religious doctrine rooted in divine authority: the source of all knowledge. Popper's method of conjecture or hypothesis is different, he says.