Logic and Theory of Knowledge 123
The second indemonstrable is that which, through a conditional and the
opposite of the consequent, draws as its conclusion the opposite of the
antecedent, for example,
If it is day, it is light.
But it is not light.
Therefore, it is not day.For the additional statement is formed from the opposite of the conse-
quent and the conclusion from the opposite of the antecedent. The third
indemonstrable is that which, through a negated conjunction and one of
the elements in the conjunction, concludes the opposite of the other
element, for example,
It is not the case that Plato is dead and Plato is alive.
But Plato is dead.
Therefore, Plato is not alive.- The fourth indemonstrable is that which, through a disjunction and
one of the disjuncts, has as its conclusion the opposite of the other,
for example,
Either the first or the second.
But the first.
Therefore, not the second.The fifth indemonstrable is that in which every argument is formed from
a disjunction and the opposite of one of the disjuncts and concludes the
other, for example,
Either it is day or it is night.
It is not night.
Therefore, it is day.According to the Stoics a truth follows from a truth, as 'it is light' follows
from 'it is day'. And a falsehood follows from a falsehood, as 'it is dark'
follows from the falsehood 'it is night'. And a truth follows from a
falsehood, as 'the earth exists' follows from 'the earth flies'. A falsehood,
however, does not follow from a truth. For 'the earth flies' does not follow
from 'the earth exists'. 82. And there are certain puzzling arguments, the
Hooded Man, the Hidden Man, the Sorites, the Horned Man, and the