It was not a "suggestion" but an analogy - basically that as we learn more, that which was previously not perceptible becomes so by the use of reason.
Correlation does not equal causation. Otherwise, we are pretty much "speaking the same language".
Even that which is (considered) non-physical/unknown can become known through its effects.
The first sentence reads:
"If something exists, whether it be visible or invisible, perceptible to the senses or not, it can be discovered and verified."
meep