The purpose of this contribution to our seminar on modelling is to make two points: 1. There is usually little point in modelling something if we do not know what it is; 2. Developing the required empirically-based generalisations in marketing is both possible and essential. To illustrate, we summarise an experimental study on pricing carried out in the UK in 1986. Our aim was to establish whether the sales response to a given price change would generalise.