The linguistic term for grammatical marking of how a speaker acquired information is evidentiality.
Evidentiality tells listeners whether a statement comes from direct observation, another person’s report, inference, or another type of evidence. In some languages, speakers must mark this information source as part of ordinary grammar, often with a verb suffix, particle or auxiliary. A language might distinguish “I saw it,” “I heard it” and “I infer it.”
Evidentiality is related to, but not identical with, mood, tense and epistemic modality. Mood concerns categories such as possibility or command; tense locates an event in time; aspect describes its internal timing. Evidentiality primarily identifies the source of knowledge, although evidential markers can also create suggestions about certainty. English usually expresses these meanings with optional phrases such as “I hear,” “apparently” or “it seems,” rather than with a compulsory grammatical category. Cross-linguistic surveys commonly estimate that about one-quarter of the world’s languages have grammatical evidentiality.