358 /l/-41
demonstrative; the demonstrative ones are those which conclude to a
non-evident conclusion by means of self-evident premisses; those that
do not have this characteristic are non-demonstrative. For example, the
argument 'if it is day, it is light; but it is indeed day; therefore, it is
light' is non-demonstrative. For the conclusion 'it is light' is self-evident.
But this argument 'if sweat is pouring through the surface [of the skin],
there are intelligible [i.e., non-sensible] pores; but sweat is indeed pouring
through the surface [of the skin]; therefore, there are intelligible pores'
is demonstrative, for the conclusion 'there are intelligible pores' is
non-evident.
- Some of the arguments concluding to a non-evident conclusion
are only progressive, leading us to the conclusion by means of the prem-
isses. Some do so both progressively and by revelation. For example,
those are [merely] progressive that seem to depend on trustworthiness
and memory, for example, 'if some god tells you that this man will
become wealthy, this man will become wealthy; but this god (assume I
am pointing to Zeus) tells you this man will become wealthy; therefore,
this man will become wealthy.' For we assent to the conclusion not
so much because the premisses necessitate it as because we trust the
pronouncement of the god. 142. Among the arguments that lead us to
the conclusion not only progressively but also by revelation are, for
example, 'if sweat is pouring through the surface [of the skin], there are
intelligible pores; but indeed the first; therefore, the second.' For the
pouring of the sweat is revelatory of the existence of the pores, because
it is already understood that moisture is not able to be conducted through
a solid body. - So, demonstration should be an argument which is both conclusive
and true with a non-evident conclusion, revealed by the force of the
premisses, and because of this a demonstration is said to be an argument
which, based on agreed premisses, according to conclusive deduction, is
revelatory of a non-evident conclusion.
So these are the terms in which they customarily clarify the conception
of demonstration.
Ch. xiii Does Demonstration Exist?
- That demonstration does not exist may be inferred from their
own words, refuting each of the components of the conception in turn.
For example, an argument is composed of propositions, and composites
are not able to exist if the parts of it do not coexist with each other, as
is self-evident in the case of a bed and similar objects. But the parts of
an argument do not coexist with each other. For when we state the first
premisse, the second premisse and the conclusion do not yet exist. And