In accepting non-perceptual sources of knowledge like inference and testimony, the Jaina writers feel it necessary to justify their view by refuting the Carvaka theory that percepdon is the only source of valid knowledge.
They ask: If a Carvaka were called upon to show why even perception should not be rejected as an invalid source of knowledge, what would he say?
He would both remain silent and thus confess that he has no reason to support his view, or hold that perception is valid because it is not misleading.
If he adopts the first course, his view is a mere ipse dixit, an opinion unsupported by reason and, therefore, not acceptable.
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If he adopts the second alternative, then he supports his view by a reason, and therefore, he is himself taking the help of inference.
Besides, if the Carvaka admits that perception is valid because it is uncontradicted and not misleading, for similar reasons inference and testimony also should be accepted.
If the Carvaka says to this, that inference and testimony are sometimes misleading, then it is possible to point out that even perception is somelimes misleading.
So the only reasonable conclusion is that any source of knowledge, be it perception or inference or testimony, should be regarded as valid in so far as it yields a knowledge that does not prove misleading.
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The criterion of validity should be the harmony (samvada) of knowledge with the practical consequences to which it leads.
Moreover, when the Carvaka denies the existence of non- perceptible objects like life-after-death, he goes beyond perception and infers the non-existence of the objects from the fact of their non-peiception.
Even when the Carvaka says about perception in general that it is valid, he goes beyond the perceived cases of perception found to be valid in the past and infers, from general similarity, something about the future unperceived cases of perception as well.
Similarly, when the Carvaka argues with his critics, he infers their thoughts from their expressions: for otherwise the Carvaka could not take part in any discussion. Hence, he Carvaka view that perception is the only valid source of knowledge is not correct.