Certainty (two degrees): In certainty we must distinguish two modes or degrees: certainty of truth and certainty of being. The first refers to a truth which is no doubt direct in relation to reason, but which is nevertheless indirect in relation to union; and it is to union that the second certainty refers. It is illogical to seek to contest this certainty, and even the first certainty, which is likewise infallible, by setting against it elements of certainty of a phenomenal or passional order; it is as if the “accidents” wanted to take issue with “substance,” or as if drops of water wanted to teach water itself what their being consists of. The certainty of the Intellect comes from the fact that it knows; no one can add anything whatsoever to its essence, or take away from it the minutest particle. [GTUFS: LogicT, The Alchemy   of the Sentiments]

Certainty / Doubt: Certainty, being an aspect of knowledge, is situated beyond the domain of the sentiments but on the individual plane it nonetheless possesses a perfume which allows us to look on it as a sentiment. One can likewise speak of a sentiment of doubt; doubt is nothing else but the void left by absent certainty and this void readily makes way for the false plenitude of error. [GTUFS: LogicT, The Alchemy of the Sentiments]