Infinite-Cofinite-Finite Trilemma
A trilemma is a trio of three statements {U,V,W}, any two of which can be true, but not all three.
Therefore for any trilemma, there are 3 deductive rules:
From U and V, deduce not-W;
From V and W, deduce not-U;
From W and U, deduce not-V.
For instance, from the trilemma:
Superman can fly;
Clark Kent can’t fly;
Superman is Clark Kent.
Deduce these three rules:
If Superman can fly;
And Clark Kent can’t fly;
Deduce: Superman is not Clark Kent.
If Clark Kent can’t fly;
And Superman is Clark Kent;
Deduce: Superman can’t fly.
If Superman is Clark Kent;
And Superman can fly;
Deduce: Clark Kent can fly.
Here is the Some-All-None trilemma:
· Some A are B;
· All B are C;
· No A are C.
From this trilemma, you can derive three deductive rules:
If some A are B;
And all B are C;
Deduce: some A are C.
If all B are C;
And no A are C;
Deduce: no A are B.
If no A are C;
And some A are B;
Deduce: some B are not C.
For example, from:
Some men are heroes;
All heroes are immortal;
All men are mortal.
Deduce:
If some men are heroes;
And all heroes are immortal;
Deduce: some men are immortal.
If all heroes are immortal;
And all men are mortal;
Deduce: no men are heroes.
If all men are mortal;
And some men are heroes;
Deduce: some heroes are mortal.
Here is an infinitary version of the Some-All-None trilemma: the Infinite-Cofinite-Finite trilemma:
· Infinitely many A are B;
· All but finitely many B are C;
· Only finitely many A are C.
From this trilemma, you can derive three deductive rules:
From: Infinitely many A are B;
And: All but finitely many B are C;
Deduce: Infinitely many A are C.
From: All but finitely many B are C;
And: Only finitely many A are C;
Deduce: Only finitely many A are B.
From: Only finitely many A are C;
And: Infinitely many A are B;
Deduce: Infinitely many B are not C.
For instance, from:
Infinitely many philosophers are Cretans;
All but finitely many Cretans are liars;
Only finitely many philosophers are liars.
Deduce:
From: Infinitely many philosophers are Cretans;
And: All but finitely many Cretans are liars;
Deduce: Infinitely many philosophers are liars.
From: All but finitely many Cretans are liars;
And: Only finitely many philosophers are liars;
Deduce: Only finitely many philosophers are Cretans.
From: Only finitely many philosophers are liars;
And: Infinitely many philosophers are liars;
Deduce: Infinitely many Cretans are not liars.
Other examples:
Infinitely many days are bliss;
All but finitely much bliss is perfect;
Only finitely many days are perfect.
There are infinitely many unicorns;
All but finitely many unicorns are goats;
Only finitely many unicorns are goats.
All but finitely many dogs go to Heaven;
Infinitely many dogs are flatterers;
Only finitely many flatterers go to Heaven.
All but finitely many cats have nine lives;
Only finitely many vampires have nine lives;
Infinitely many cats are vampires.
Infinitely many good deeds are wise;
All but finitely many wise deeds go unpunished;
Only finitely many good deeds go unpunished.
All but finitely many Scots are canny;
All but finitely many ghosts are uncanny;
Infinitely many Scots are ghosts.
All but finitely many aliens play video games;
Only finitely many angels play video games;
Infinitely many aliens are angels.
Only finitely many ducks waltz;
All but finitely many officers waltz;
Infinitely many officers are ducks.