general ability, force of character, or knowledge of
administration than the head of administration of a great city like New
York or Berlin. The latter we know to be well administered, the
former--well, let us say, less so. The whole difference is in the
systems. Apply the Berlin system to New York, and you will get Berlin
results.

Here the writer wholly ignores all sorts of active causes for this
difference: Berlin has a tolerably homogeneous population, New York the
most heterogeneous in the world; Germans by nature respect law and
authority, and hanker for centralization; Americans make and break laws
light-heartedly, and are restive under authority; and one might easily
go further.

Arguments that national prosperity has followed a higher or a lower
tariff are especially apt to be vitiated by this error. It is not that
the tariff has no relation to the prosperity, but that there are other
causes intermingled with it which may have had more immediate effect. A
bad grain crop or a season of reckless speculation may obliterate all
the traceable causes of a change in the tariff. Arguments from motive,
too, are apt to fall into this error. It is notorious that human motives
are mixed. If you argue that a whole class of business organizations are
evil because they have been formed solely for the purpose of making
inordinate and oppressive profits, you leave out of sight a motive which
is strong among American business men--the interest in seeing a great
business more efficiently managed, and the desire to exercise power
beneficently; and your argument suffers from its illegitimate assumption
of a simple cause. So in the same way if you are arguing for or against
the advantages of the elective system in a school or a college, or of a
classical education, or of athletics, it would be folly to assume that
any one cause or effect covered the whole case. Whenever in an argument
you are trying to establish any such large and complex fact, you must be
wary lest you thus assume a single cause where in reality there are a
legion of causes.

41. Deductive Logic--the Syllogism. Deductive logic, as we have seen,
deals with reasoning which passes from general principles to individual
cases. Its typical form is the syllogism, in which we pass from two
propositions which are given to a third, the conclusion. Of the two
former one is a general principle, the other an assertion of a
particular case. The classic example of the syllogis