Summary: We report on ongoing research on the semantic and pragmatic factors that influence the interpretation of co-speech spontaneous gestures. We extend the semantic theory introduced by Giorgolo in [1] by proposing a pragmatic principle that controls the felicitousness of spontaneous gestures in different linguistic contexts. The principle is based on the idea of rationality in communication and will result in an extension of the gricean Maxim of Quantity [2]. We also present an experiment that we designed to test the predictions of the combined semantico-pragmatic principles.