YOUR MIND AND HOW TO USE IT/PART 25
CHAPTER XXV.
Reasoning.
REASONING,
the third great step in thinking, may be said to consist of ascertaining new
truths from old ones, new judgments from old ones, unknown facts from known
ones; in short, of proceeding logically from the known to the unknown, using
the known as the foundation for the unknown which is sought to be known. Gordy
gives us the following excellent definition of the term: "Reasoning is the
act of going from the known to the unknown through other beliefs; of basing
judgment upon judgments; reaching beliefs through beliefs." Reasoning,
then, is seen to be a process of building a structure of judgments, one resting
upon the other, the topmost point being the final judgment, but the whole
constituting an edifice of judgment. This may be seen more clearly when the
various forms of reasoning are considered.
Immediate
Reasoning.
The
simplest form of reasoning is that known as "immediate reasoning," by
which is meant reasoning by directly comparing two judgments without the
intervention of the third judgment, which is found in the more formal classes
of reasoning. This form of reasoning depends largely upon the application of the
Three Primary Laws of Thought, to which we have referred in a previous chapter.
It
will be seen that if (a) a thing is always itself, then
(b) all that is included in it must partake of its nature. Thus, the
bird family has certain class characteristics, therefore by immediate reasoning
we know that any member of that family must possess those
class characteristics, whatever particular characteristics it may have in
addition. And we likewise know that we cannot attribute the particular characteristics,
as a matter of course, to the other members of the class. Thus, though all
sparrows are birds, it is not true that all birds are sparrows. "All
biscuits are bread; but all bread is not biscuit."
In
the same way we know that a thing cannot be bird and mammal at the same time,
for the mammals form a not-bird family. And, likewise, we know that
everything must be either bird or not bird, but that being not
bird does not mean being a mammal, for there are many other not-bird things
than mammals. In this form of reasoning distinction is always made between
the universal or general class, which is expressed by the
word all, and the particular or
individual, which is expressed by the word "some." Many persons
fail to note this difference in their reasoning, and fallaciously reason, for
instance, that because some swans are white, all swans
must be so, which is a far different thing from reasoning that if all is
so and so, then some must be so and so. Those who are
interested in this subject are referred to some elementary text-book on logic,
as the detailed consideration is too technical for consideration here.
Reasoning
by Analogy.
Reasoning
by analogy is an elementary form of reasoning, and is the particular kind of
reasoning employed by the majority of persons in ordinary thought. It is based
upon the unconscious recognition by the human mind of the principle which is
expressed by Jevons as: "If two or more things resemble each other in
many points, they will probably resemble each other in more points."
The same authority says: "Reasoning by analogy differs only in degree from
that kind of reasoning called 'generalization.' When many things resemble
each other in a few properties, we argue about them by
generalization. When a few things resemble each other in many
properties, it is a case of analogy."
While
this form of reason is frequently employed with more or less satisfactory
results, it is always open to a large percentage of error. Thus, persons
have been poisoned by toadstools by reason of false analogous reasoning that
because mushrooms are edible, then toadstools, which resemble them, must also
be fit for food; or, in the same way, because certain berries resemble other
edible berries they must likewise be good food. As Brooks says: "To infer
that because John Smith has a red nose and is also a drunkard, then Henry
Jones, who also has a red nose, is also a drunkard, would be dangerous
inference. Conclusions of this kind drawn from analogy are frequently
dangerous." Halleck says: "Many false analogies are manufactured, and
it is excellent thought training to expose them. The majority of people think
so little that they swallow these false analogies just as newly-fledged robins
swallow small stones dropped into their mouths."
Jevons,
one of the best authorities on the subject, says: "There is no way in
which we can really assure ourselves that we are arguing safely by analogy. The
only rule that can be given is this: That the more closely two things resemble
each other, the more likely it is that they are the same in other respects,
especially in points closely connected with those observed. In order to be
clear about our conclusions, we ought, in fact, never to rest satisfied with
mere analogy, but ought to try to discover the general laws governing the case.
* * * We find that reasoning by analogy is not to be depended upon, unless we
make such an inquiry into the causes and laws of the things in question that we
really employ inductive and deductive reasoning."
Higher
Forms of Reasoning.
The
two higher forms of reasoning are known, respectively, as (1) inductive
reasoning, or inference from particular facts to general laws; and (2)
deductive reasoning, or inference from general truths to particular truths.
While the class distinction is made for the purpose of clear consideration, it
must not be forgotten that the two forms of reasoning are generally found in
combination. Thus, in inductive reasoning many steps are taken by the aid of
deductive reasoning; and, likewise, before we can reason deductively from general
truths to particular ones we must have discovered the general truths by
inductive reasoning from particular facts. Thus there is a unity in all
reasoning processes as there is in all mental operations. Inductive reasoning
is a synthetical process; deductive reasoning, an analytical one.
In the first we combine and build up, in the latter we dissect and separate.
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