The linguistic function of the Colloquial Singapore English (CSE) particle lah has been characterized variously as a marker to convey solidarity, warmth and informality; an attenuation or emphasis marker; an assertion marker; and an accommodation marker. As the particle can be pronounced using several pitch contours, the particle has generally been analyzed as either a set of homonymic variants that are distinguished by pitch and function, or a unitary particle that has the same meaning despite tonal differences. However, I argue against both approaches – the former conflates pragmatic function and semantic meaning, while the latter ignores the systematic differences in function that correlate with tonal differences. Instead, using a relevance-theoretic framework, I propose that the different pragmatic functions of lah result from the interaction between its unitary semantic meaning and the effect of pitch as signals of modality, specifically a falling tone that marks declaratives/imperatives and a rising tone that marks interrogatives. The advantages of this approach are also discussed in relation to another CSE particle hor, which similarly differs in pragmatic function depending on whether it is pronounced with a falling or rising tone.