A piece of information expressed in a statement may have been obtained from different sources. The languages of the world all differ in the way they demonstrate the source of the information expressed. In Turkish the source of information is marked by -mIs in verbs and by -(y)mIs in nouns and compound inflections. Both of these suffixes suggest that the information expressed has been obtained indirectly. This may happen through a variety of ways such as seeing, hearing, inferring, realizing, assuming, smelling, touching, and tasting. Furthermore, the forms indicating indirect source of knowledge in standard Turkish are used in different ways in different dialects. Some Turkish dialects use the -mIs suffix as a direct past tense marker, doing away with the indirect meaning in standard Turkish. Some others, on the other hand, do not make wide use of this suffix at all. It is also possible to come across dialects where the indirect meaning is expressed through suffixes other than the standard -mIs. This article looks closely into these issues related to evidential categories in Turkish.