1.  Maple trees shed their leaves in winter.
  2.  Dogs bark.
  3.  Kettles are made of iron.
  4.  Grasshoppers jump.
  5.  Giraffes have long necks.
  6.  Raccoons sleep in the daytime.
  7.  The sun will rise to-morrow.
  8.  Examinations are not fair tests of a pupil’s knowledge.
  9.  Honest people are respected.
 10.  Water freezes at 32 deg.  Fahrenheit.
 11.  Boys get higher standings in mathematics than girls do.

It is at once evident that we believe a proposition such as one of these, because we have known of many examples.  If we reject any of the propositions it is because we know of exceptions (we have seen kettles not made of iron), or because we do not know of instances (we may never have seen a raccoon, and so not know what he does in the daytime).  The greater the number of cases which have occurred without presenting an exception, the stronger our belief in the truth of the proposition (we expect the sun to rise because it has never failed).

The process by which, from many individual cases, we establish the truth of a proposition is called +inductive reasoning+.

+175.  Establishing a General Theory.+—­A general theory is established by showing that for all known particular cases it will offer an acceptable explanation.  By investigation or experiment we note that a certain fact is true in one particular instance, and, after a large number of individual cases have been noted, and the same fact found to be true in each, we assume that such is true of all like cases, and a general law is established.  This is the natural scientific method and is constantly being made use of in pursuing scientific studies.  By experiment, it was found that one particular kind of acid turned blue litmus red.  This, of course, was not sufficient proof to establish a general law, but when, upon further investigation, it was found to be true of all known acids, scientists felt justified in stating the general law that acids turn blue litmus red.

In establishing a new theory in science it is necessary to bring forward many facts which seem to establish it, and the argument will consist in pointing out these facts.  Frequently the general principle is assumed to be true, and the argument then consists in showing that it will apply to and account for all the facts of a given kind.  Theories which have been for a time believed have, as the world progressed in learning, been found unable to account for all of a given class of conditions.  They have been replaced, therefore, by other theories, just as the Copernican theory of astronomy has displaced the Ptolemaic theory.

Our belief may be based upon the absence of facts proving the contrary as well as upon the presence of facts proving the proposition.  If A has never told an untruth, that fact is an argument in favor of his truthfulness on the present occasion.  A man who has never been dishonest may point to this as an argument in favor of placing him in a position of trust.  Often the strongest evidence that we can offer in favor of a proposition is the absence of any fact that would support the negative conclusion.