In medieval epistemology, science -- scientia -- is knowledge. Knowledge is knowledge of universal truths which are true of necessity. (Hacking, The Emergence of Probability , p. 20)Science was restricted to knowledge of universal, necessary truths that are either axioms or deducible therefrom with demonstrative certainty. The deliverances of the senses had no significant role. According to Douglas Lane Patey (whose book contains a wealth of info on this topic), the sciences typically included theology, metaphysics, mathematics, and physics (Patey, From Rhetoric to Science, [Cambridge, UK: Cambridge University Press, 1984], p. 11).
This knowledge-opinion distinction appeared in some of the earliest logic books to be published in English. Here are two examples:
All these intellectual habits are contained under a certain and most sure knowledge, which is always true, for uncertain knowledge is sometimes true, and sometimes false: whereto belongeth opinion, suspicion, conjecture, and such like. (Thomas Blundeville, The Art of Logike , p. 28)
A true axiome is ... Contingent, when it is in such sort true, that it may also at sometime be false. This is called opinion' (pp. 156-7). 'These Illations being pronounced by God, have always a necessary veritie .... [B]ut these propositions being pronounced by man, doe containe (at the best) but opinion, contingent, and coniectur [conjecture] all knowledge. (Thomas Spencer, The Art of Logick , p. 232)While inferior to knowledge, opinion wasn't relegated to some purely subjective or non-cognitive dustbin, and it was taken to be amenable to some form of rational support. In fact, whole disciplines, such as law, medicine, and history, were regarded as trading in opinions rather than scientific knowledge. So, the medievals (and many renaissance and early modern scholars) took it to be a matter of some importance to draw up canons for the intellectually responsible management of opinions. In this endeavour, they built on Aristotle's (and Cicero's) dialectical and rhetorical studies.
For the most part, even as the understanding of science changed (becoming more empirical), opinion retained its old status. Here's a passage from Locke's Essay:
The entertainment the mind gives this sort of proposition is called belief, assent, or opinion, which is the admitting or receiving any proposition for true, upon arguments or proofs that are found to persuade us to receive it as true, without certain knowledge that it is so. (Locke, An Essay Concerning Human Understanding, Ch. 15: 'Of Probability')As in the medievals, opinions aren't so bad. Sure, they're not knowledge, but they're there when we need 'em and they get us through the day. Just be sure to trust one only when it's vouchsafed by some argument. As Isaac Watts put it,
Where we cannot find weight enough on either side to determine the scale with sovereign force and assurance we must content ourselves perhaps with a small preponderation. This will give us a probable opinion and those probabilities are sufficient for the daily determination of a thousand actions in human life and many times even in matters of religion. (Watts, The Improvement of the Mind , p. 207)It comes as some surprise, then, to find Joseph Glanvill's righteous fulminations against opinion in 'The Vanity of all Dogmatizing' (1661). This work includes the following magnificent lines:
Verisimilitude and Opinion are an easie purchase; and these counterfeits are all the Vulgars treasure: But true Knowledge is as dear in acquisition, as rare in possession (p. 64). ... Opinions are the Rattles of immature intellects, but the advanced Reasons have out-grown them. True knowledge is modest and wary (p. 226). ... I Expect but little success of all this upon the Dogmatist, his opinion'd assurance is paramont to Argument, and 'tis almost as easie to reason him out of a Feaver, as out of this disease of the mind (p. 224). ... 'Tis zeal for opinions that hath fill'd our Hemisphear with smoke and darkness (p. 229). ... Thus Opinions have rent the world asunder, and divided it almost into indivisibles (p. 231).Glanvill associates opinion with the wars over conflicting religious and political opinions. In future posts, I'll try to identify other reasons for the growing pejorative connotations of 'opinion' in the the seventeenth and eighteenth centuries.