 |
Basic Logic Concepts |
|
Basic Logic Concepts |
 CATEGORICAL
SYLLOGISMS |
 A
categorical syllogism is an argument consisting of exactly three categorical
propositions (two premises and a conclusion). In the entire syllogism
there appears only and exactly three categorical terms with each being
used twice.
One term is the subject of
the conclusion. It is the minor term. It also appears in minor
premise. One term is the predicate of the conclusion and it is called
a major term. This term also appears in major premise. The
third term does not appear in the conclusion but must appear once in each
premise.
Major Premise ------ No robins are cats |
| Minor Premise ------- Some birds are robins |
| Conclusion ------ Therefore some birds are not cats |
 Be
patient!!! The first premise is called the major premise. It
affirms a relation between its middle (robin) and major term (cats).
The second premise links the middle (robin) and minor (birds) terms.
In the conclusion it is clear that "some birds are not cats." Again,
the major term is cats. It must appear as predicate term of conclusion.
One
simple way to see conclusion is to strike like terms in major and minor
premise (e.g. robins).
This leaves you with deductive conclusion. "some birds" and "no are cats."
Again, some birds are not cats. |
|
There
are 256 different kinds of categorical syllogisms. You do not need to know
them all. But know that most legal arguments can be broken down into
syllogistic form (though this "formalism" is not the all of legal judgment).
Another common form employs "all" and "no" rather than "some." |
|
Major Premise ---- All men are human |
| Minor Premise ---- No humans are souless beings |
| Therefore ----- No souless beings are men |
|
Warning.
In
order for an argument
to be valid, we need only say "if premises" were true, conlclusion would
follow. its validity is merely logical. Whether the premises are
indeed true is another matter. So you can show the "illogic" of a conclusion
by logical analogy. If you can think of a like syllogism to the one
you test, and in the analogy both premises are true, you have a faulty
analogy as well as a faulty original syllogism. Example: |
| Major Premise ------- All thinkers are professors |
| Minor Premise -------- All thinkers are logicians |
| Therefore ------- All logicians are professors |
| This may look right at first by just striking like term in major and minor premise (thinkers). But look at analogy that tests the above: |
| Major Premise ----- All terriers are dogs |
| Minor Premise ------ All terriers are mammals |
| Therefore ----- All mammals are dogs |
You test by seeing that while both premises ARE true, you know conclusion
is fase. HENCE, this tells you that ANY syllogism of this Form also
will be invalid. E.g., we know all logicians too are not professors. |
 Push
on the Pearl to be Linked to an excellent site on basic logic. |
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