The two studies presented in this paper concern the Italian epistemic marker mi sa [lit. to me it knows], which seems to have no equivalent in other European languages and has received very little attention in the literature. No analysis of the occurrences of mi sa in contemporary spoken corpora can be found (first gap) as well as no investigation on the epistemic relationship between mi sa and (1) the other modal expressions that use the verb sapere [to know] in the first person singular of the simple present, i.e., so [I know], non so [I do not know], non so se [I do not know whether] as well as (2) its supposed synonyms credo [I believe] and penso [I think] (second gap). The two studies are closely intertwined, the first being an exploratory, qualitative pilot study for the second. Study 1 aims to fill the first gap through the analysis of the contemporary Italian spoken corpus KIParla. The quantitative and qualitative analyses revealed five types of occurrences (theoretically reducible to two main ones), the most numerous of which are 'mi sa che + proposition'. Study 2 aims to fill the second gap through a questionnaire administered online. The quantitative and statistical results showed the epistemic relationships between the six markers: for the majority of the participants, in the epistemic continuum that goes from unknowledge to uncertainty and then to knowledge, (1) non so refers to unknowledge; non so se, mi sa, credo and penso refer to uncertainty; so refers to knowledge; (2) mi sa, credo, penso confirm to be synonyms; (3) non so se is evaluated as much more uncertain than mi sa, credo, penso. These four epistemic markers seem to occupy a different position along the uncertainty continuum ranging between two poles: doubt (high uncertainty) and belief (low uncertainty).