Tsou (also known as Northern Tsou) differs from the other Formosan languages in having developed a complex system of case markers - divided into two sets: nominative (?e, si, ta, na) and oblique (ta, to, no) - which "localize" an object in relation to the speaker/hearer. Traditionally, they are classified according to the following parameters: proximity, visibility and definiteness.

It is our purpose to examine in the present paper the system of Tsou case markers, focalizing our attention on the semantic level.

We first present briefly the structure of the language as well as the syntactic properties of case markers. After having shown the limits of Tung's (1964) analysis, we argue that the speaker adjusts or calculates the position of the object (referred to) in relation to the "here-me-now" of the speech situation. Such an analysis enables us to account for a large range of data. It also enables us to account for (1) the possible and impossible substitutions of case markers with one another and (2) the permissible and non-permissible co-occurrences of case markers with aspectual particles.