In Puyuma, the marker i- is used to express meanings of wearing, possession, instrumentality, and existence. The purpose of this paper is to investigate how these different meanings can be related and what the developmental path is. It is suggested that the original meaning of this marker is ‘carry, wear’, and that this was later grammaticalized to give the meanings of possession and instrumentality. The meaning of existence is the result of a later development. Evidence from other Formosan languages also shows that the morpheme *Si-, meaning ‘wear, carry’, can be reconstructed to Proto-Austronesian, and thus supports our hypothesis.