Adopting a central feature of Stoic epistemology, Descartes treated belief as action that might be undertaken wisely or rashly, and enunciated a method for avoiding false belief, a discipline of the will “to include nothing more in my judgments than what presented itself to my mind with such clarity and distinctness that I would have no occasion to put it in doubt.” He called such acts of the will “affirmations,” i.e., acts of accepting sentences or propositions as true. (Essay 2 argues against “cognitive” uses of decision theory to choose among such replacements of considered probabilities by specious certainties.)

What do “belief,” “acceptance,” and “affirmation” mean in this context? I don't know. I'm inclined to doubt that anyone else does, either, and to explain the general unconcern about this lack of understanding by familiarity el the acceptance metaphor masquerading as intelligibility, perhaps as follows: “Since it's clear enough what's meant by accepting other things – gifts, advice, apologies – and it's clear enough what's meant by sentences' being true, isn't it clear what's meant by accepting sentences as true? Doesn't Quine make ‘holding’ sentences true the very pivot of his epistemology? And isn't affirmation just a matter of saying ‘Yes’?”

The (“Bayesian”) framework explored in these essays replaces the two Cartesian options, affirmation and denial, by a continuum of judgmental probabilities in the interval from 0 to 1, endpoints included, or – what comes to the same thing – a continuum of judgmental odds in the interval from 0 to ∞, endpoints included.