In earlier issues of Mountain Research and Development (Vol. 5, Nos. 2 and 3), Thompson and Warburton developed an institutional approach to development in the Himalayan region: an approach that, in treating the institutions and the perceptions they generate as the facts, largely dissolved away the physical constraints in a sea of uncertainty. In this article, we try to complete the exploratory circle by bringing nature-the physical constraints-back into our cultural picture.All institutions, sooner or later, bump against these constraints; the local farmers sooner, the international agencies later. Learningreadjustments in systems of knowledge -then takes place. Nature, in effect, forces the different systems of knowledge that are promoted by different institutions into conversation with one another. The present challenge is to convert that conversation from monologue to dialogue. T8t ou tard, les institutions concern~es doivent faire face h ces contraintes, les fermiers d'abord, puis les agences internationales. C'est alors que l'apprentissage se produit, c'est-k-dire un reajustement des systhmes de connaissance. En effet, la nature force les diff&rents systhmes de connaissance embrass~s par diverses institutions t s'adapter les uns aux autres. Ce qu'il reste i faire est de promouvoir une communication vtritable entre ces systhmes, au b6ndfice de tous.