"Habit" is not an easy term in Peirce's epistemology: on the one hand it often signifies the rule of action that is attained with the fixation of belief (1877) [EP 1: 109–123]; on the another hand, it is also described as an almost instinctual process that determines further reasonings, the element "by virtue of which an idea gives rise to another" (1873) [CP 7.354]. Stressing the apparently wide separation between these two traits of habit in the epistemic continuum between doubt and belief, we will be able to illustrate (a) a knowledge-based kind of habit, for the analysis of which we will also exploit Gibson's concept of "affordance" (1950), which also plays a pivotal role in the justification of the agent's own beliefs; and (b) an ignorance-based kind of habit, which will be proved as necessary for the beginning of thought, and which is at the base of the ampliative reasoning, condensed in another Peircean key topic (often qualified as "instinctual" in his writings): abduction.