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to the specific, from theory to data. The book of nature is grounded in induction—the process of drawing generalized conclusions from specific statements, or arguing from the specific to the general, from data to theory. It would be oversimplified and unrealistic to describe any one person or tradition as practicing pure induction or pure deduction, for none of us operates in a vacuum without inputs from many sources, and it is impossible to operate without both modes of thinking. Data and theory go hand in hand. Nevertheless, there are periods in the history of science when one has been emphasized more than the other, and Galileo and his fellow revolutionaries were butting up against a deep tradition in deduction.

Figure 14. The Book of Authority Triumphs over the Book of Nature

So powerful was the tradition of respecting the authority of the ancients, that “naturalists” were little more than scribes who copied the copies of previous copiers from some long-ago original source. The half-man / half-beast creature called the “Lamia” (a) and the half-man / half-plant creature called the “Mandragora” (b) were both staples of sixteenth- and seventeenth-century works. The two artist-naturalists sketching an actual plant (c) mark a sea change in the shift from the book of authority to the book of nature. Lamia from Edward Topsell’s 1607 The Historie of Foure-footed Beastes. Mandragora from the 1485 German Herbarius. The artist-naturalists from Fuchs’s 1542 De Historia Stirpium. All are reprinted from ALAN DEBUS, MAN AND NATURE IN THE RENAISSANCE (CAMBRIDGE: CAMBRIDGE UNIVERSITY PRESS, 1978), PP. 36, 44, 45.

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The pull of Aristotelian logic tied to deductive reasoning was compelling and hard to overcome. In the early 1600s, for example, while Galileo was making his first telescopic observations, it was suggested that space consisted literally of nothing—a vacuum. But how, then, would the planets move through it? According to Aristotle, an object moved through air or space by “impetus,” in which air or “ether” passes and envelops the object, thereby pushing it from behind and giving it thrust. Just as an arrow moves through the atmosphere by the air enveloping it and pushing it from behind, so, too, do planets move through space with the ether surrounding them and pushing them from behind. Without the ether no thrust could exist to push a planet through space. The planets move, ergo no vacuum. Ether, thereafter, became the fifth element—along with earth, water, air, and fire—and belief in it persisted all the way into the twentieth century, until the experiments on the speed of light by physicists Albert Michelson and Edward Morley were fully accepted. Such is the endurance of belief, even in the sciences.

In 1620, a staunch challenge to Aristotle’s deductive methodology was proffered by the English philosopher Francis Bacon in his book Novum Organum. This “new instrument” was the empirical or observational method. Rejecting both the unempirical tradition of scholasticism and the Renaissance quest to recover and preserve ancient wisdom, Bacon sought a blend of sensory data and reasoned theory, with emphasis on data and caution about theory. Ideally, he proposed, one should begin with observations then formulate a general theory from which logical predictions could be made. Bacon outlined how the mind works in this regard:

There are and can be only two ways of searching into and discovering truth. The one flies from the senses and particulars to the most general axioms, and from these principles, the truth of which it takes for settled and immovable, proceeds to judgment and to the discovery of middle axioms. The other derives axioms from the senses and particulars, rising by a gradual and unbroken ascent, so that it arrives at the most general axioms last of all. This is the true way, but as yet untried.20

Impeding Bacon’s goal, however, were psychological barriers that colored clear judgment of the facts, of which he identified four types: idols of the cave (individual peculiarities), idols of the marketplace (limits