The theorems given for practice in logic books are useful dialectic
material, but they do not fully illustrate all the categories.
Logicians have no definite categories, and in selecting examples they
are unconsciously biassed in favour of those that can be most easily
interpreted to signify classification. The really generalistic
examples are rare; the most are judgments of inherence, admitted in
virtue of the assumption that inherent properties can--when it
is needful to preserve the traditional notion of predication--be
considered class-ideas. Theorems in perspection and concretion we do
not expect to find in logic books, for these, in so far as they are
distinct from association, are categories peculiar to the Berkeleyan
philosophy.
Whately has the following example in association--'Lias lies above red
sandstone; red sandstone lies above coal; therefore lias lies above
coal.' No doubt Whately would, in syllogising this, have changed the
propositions to 'Red sandstone is lying,' &c., and have assumed that
'lying above coal' is a class to which red sandstone belongs.
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