An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

THE GENERAL NATURE OF INDUCTION. 239
Ex. 3.
Smoke that goes downwards is heavier than air ;
Particles of moisture are heavier than air ;
Therefore particles of moisture are in the descending
smoke.
This conclusion is probable; for the cause would
naturally act in the way suggested. For the other
example, we may find a rather stronger justification.
Ex. 4.
Protective resemblances naturally increase through
series of species from slighter to closer resem
blance ;
The resemblances in question increase in genus
x from slighter to closer resemblance to y ;
Therefore the resemblances in question show impor
tant signs of being protective.
The student should notice, finally, that our ordinary
perceptive judgments are enthymemes in fig. ii., when
their implication is expressed in words :
Ex. 5.
An oak-tree has such and such appearances ;
This object has the same appearances ;
Therefore this object is an oak-tree.
Again :
My brother has such and such an appearance ;
That person has the same appearance ;
Therefore that person is my brother.
Most of our mistakes in identification arise from the
formal invalidity of the inference into which the per
ceptive judgment may be expanded.
(c) In the first figure, as we said, the enthymeme
becomes a formally valid syllogism whose truth depends