deviate right or left, and
that there is _no reason_ for its going one way more than the other: to
which the answer is, that, apart from experience, we could not know
whether or not there were a reason. Geometers often fall into this
Fallacy.

4. _The differences in nature must correspond to our received
distinctions_ (in names and classifications). Thus, the Greeks thought
that, by determining the meanings of words, they ascertained facts.
Aristotle usually starts with 'We say thus or thus.' So, with the
_Doctrine of Contrarieties_, in which the Pythagoreans and others
assumed that oppositions in language imply similar ones in nature.
Hence, too, the ancient belief in the essential difference between the
laws of things terrestrial and things celestial, and in man's
incapability of imitating nature's works. Bacon's error (which vitiates
his inductive system) was analogous, in looking (either through his
eagerness for practical results, or a lingering belief that causes were
the sole object of philosophy) for the cause of given effects rather
than the effects of a given cause. Hence sprang his tacit assumption
(and that in enquiries into the causes of a thing's sensible qualities,
where it was especially fatal), that in all cases, e.g. of heat or cold,
the _forma_, or set of conditions, is _one_ thing. A similar notion,
viz. that each property of gold, as of other things, has its one
_forma_, produced the belief in Alchemy.

5. The conditions of a phenomenon often do resemble the phenomenon
itself, e.g. in cases of Motion, Contagion, Feelings; but it is a
Fallacy to suppose that _they must or probably will_. By this fancied
law men guided their conjectures. Thus, the _Doctrine of Signatures_
was, that substances showed their uses as medicines by external
resemblance, either to their supposed effect, or to the disease. So, the
Cartesians, and even Leibnitz, argued, that nothing physical but
previous motion could account for motion, explaining the human body's
voluntary motions by Nervous Vibrations or by Animal Spirits. Hence,
too, the inference that there is a correspondence between the physical
qualities of the cause, and like or like-named ones, either of the
phenomenon (e.g. between sharp particles and a sharp taste), or of its
effects (e.g. between the redness of Mars, and fire and slaughter as
results of that planet's influence). In metaphysics, the Epicureans'
doctrine of _species sensibiles_, and the moderns' o