Hetvabhasa

This is the term for a fallacious argument.
For a valid inference (anumana), certain
conditions must be met, or the inference
will be invalid. The accepted form for an
inference has three central terms: the first
is a hypothesis (pratijna), which contains
a subject class (paksha) and a thing to be
proved (sadhya); the second is a reason
(hetu) giving evidence for the hypothesis;
and last come examples (drshtanta),
which give further evidence for the
hypothesis. In the stock example, the
hypothesis that “there is fire on this
mountain” is making a certain claim
(sadhya)—namely, that there is fire—
about a certain class of things (paksha)—
namely, this mountain. The inference’s
second part gives the reason (hetu)
“because there is smoke on this mountain,” which also makes a claim about the
subject class—namely, this mountain.
One condition necessary for a valid
inference is for the subject class to
fall within the reason given, so that in
all cases the reason would apply to it.
The statement “there is fire on this
mountain because there is smoke on
that mountain” is an example where
the subject class and the reason given
are clearly separate.
Yet the most important condition for a
valid inference is that the reason given
must account for every case of the thing
to be proved, such that it cannot be
explained in any other way. This is known
as pervasion (vyapti) and is a critical test
for the hetu. For the Indian logicians,
claiming that smoke implied the presence
of fire was a valid inference, since smoke
was always produced by fire.
On the other hand, the claim that fire
implied the presence of smoke was
invalid. This was because the logicians
could name a case in which fire was not
invariably accompanied by smoke, and
thus failing this requirement of “pervasion”—the case of the red-hot iron ball,
which was considered fiery, but not
smoky. This counterexample is known as
an upadhi (“obstruction”). It gives an
example when one thing does not
inevitably bring another, and thus shows
that the hetu fails to pervade the sadhya,
since there is a class of fiery things that do
not smoke. For further information see
Karl H. Potter (ed.), Presuppositions of
India’s Philosophies, 1972.