listen to the pronunciation of doubtable
Englisch - Englisch
Fearsome; redoubtable
Capable of being doubted; doubtful; dubious; dubitable. See usage notes below

Descartes adopts the tool of a radical skepticism, submitting to question established beliefs, exposing them to the test of doubt, breaking them down when they prove doubtable.

Worthy of being feared; redoubtable
{s} questionable, may be doubted
Capable of being doubted; questionable