Indeed, not for many years yet do we come upon any positive evidence of revival.

For instance, during language acquisition, human children are largely only exposed to positive evidence.

There are patterns in all natural languages that cannot be learned by children using positive evidence alone.

Children are only ever presented with positive evidence for these particular patterns.

This is basically that children cannot use only positive evidence to learn language.

On the other hand, we have as yet no positive evidence that any crime has been committed.

But there was no positive evidence, according to the reporters.

Not unless you get positive evidence that Jane or one of the other women is alive.

There is no positive evidence that Jesus saw anything wrong with the sexism of his day.

The words "we saw" are positive evidence that the author was a contemporary.