~}{~GREEK SMALL LETTER IOTA WITH OXIA~}{~GREEK SMALL LETTER ALPHA~} of
Aristotle executed from a Christian point of view. In respect to the
logical method there was a general agreement of opinion, but difference of
system arose in the metaphysical. The form that the problem of science
then assumed was peculiar. Instead of examining the data from which
deduction starts, with a view of finding their subjective certainty as
thoughts, the inquirers strove to settle the problem of their objective
nature as things. The question asked was this: Are the genera and species
which the mind contemplates, in its attempts to classify and interpret
phenomena, real in nature, or produced only by human thought and speech? A
comparison with the modern mode of investigation will explain the
importance which the question possessed, and the reason why it monopolized
the entire field of inquiry.

The progress of discovery has forced upon us a subdivision of the sciences
into two classes, unknown in the middle ages; in one of which we discover
causes; in the other, in which we are unable to find causes, we rest
content with classification by species and genera. In the former we
discover antecedents, in the latter types.(257) But in mediaeval science,
as in Greek, the latter class was regarded as the sole form of all perfect
science. Hence the reason will appear why the question as to the true
nature of genera and species had a monopoly of the field of inquiry; and
also why the theory of predication was exalted into the most important
part of logic.(258) Those who thought that genera had a real existence as
essences apart from man's mind and from nature, were denominated Realists:
those who denied to them any real existence, and considered them to be a
common quality labelled by a common name, were Nominalists: those who held
the intermediate view, and assumed them to exist, not only as artificial
names but also as general classes in the human mind, were Conceptualists.
With the realist, classification was not arbitrary, but true and
determined for man. With the nominalist and conceptualist it was created
by man, and amenable to correction.

The question, though now relegated from metaphysical to physical science,
has still sufficient importance to enable us to perceive likewise the
reason why these different theories could be the means of dividing men
into parties. The bitterness with which a zoological inquiry of analogous
character into the