Evidentiality

In linguistics, evidentiality is, broadly, the indication of the nature of evidence for a given statement; that is, whether evidence exists for the statement and if so what kind. An evidential (also verificational or validational) is the particular grammatical element (affix, clitic, or particle) that indicates evidentiality. Languages with only a single evidential have had terms such as mediative, médiatif, médiaphorique, and indirective used instead of evidential. Evidential is a meaning of nature and statement that is whether evidence exists for the statement and what kind of evidence exists.

All languages have some means of specifying the source of information. European languages (such as Germanic and Romance languages) often indicate evidential-type information through modal verbs (Spanish: deber de, Dutch: zouden, Danish: skulle, German: sollen) or other lexical words (adverbials) (English: reportedly) or phrases (English: it seems to me).

Some languages have a distinct grammatical category of evidentiality that is required to be expressed at all times. The elements in European languages indicating the information source are optional and usually do not indicate evidentiality as their primary function — thus they do not form a grammatical category. The obligatory elements of grammatical evidentiality systems may be translated into English, variously, as I hear that, I see that, I think that, as I hear, as I can see, as far as I understand, they say, it is said, it seems, it seems to me that, it looks like, it appears that, it turns out that, alleged, stated, allegedly, reportedly, obviously, etc.

...
Wikipedia