This paper studies the semantics of Cantonese approximative sentence-final particles mat1zai3 ‘MATZAI’ and gam3zai3 ‘GAMZAI’, which have their meaning predominantly determined by the polarity of the proposition. I argue that polarity sensitivity of mat1zai3 and gam3zai3 is due to their semantics as scalar operators, with their interpretations governed by two components. The proximal component requires the realization of the proposition come close to the proposition prejacent to mat1zai3 and gam3zai3 to be true. The polar-minimal component not only reverses the polarity of the prejacent proposition, but requires the proposition to mark a point in a minimal or small interval from the low-end or the high-end of the scale. Adapting a scalar model, the close relation of mat1zai3 and gam3zai3 with polarity can be accounted for by the two semantic properties encoded in polarity items in relation to the informative value. Approximatives require scalar ordering from top-end/high-end to bottom-end/low-end, or from bottom-end/low-end to top-end/high-end of the scale, in order to satisfy the requirement of giving high informative value. The scalar analysis is preliminarily extended to English approximatives to provide a unified analysis under a scalar model for approximatives in natural language.