ABSTRACT
Our aim here is to give the reader the conceptual bases necessary for using without difficulty the systems presented. But for a rigorous classification of soils it is necessary to refer to works that have been written for that purpose. Simplifications have been introduced to summarize very voluminous technical manuals to a few pages. There are differences in principle between the classifications, the taxonomies, the reference bases and the nomenclatures. This issue is considered in detail in the larger French edition of this book. The genetic classifications involve external factors (for example, climate) or at least the processes whose occurrence in the soil under study leads to an interpretation (for example, decarbonatation). They can be contrasted to objective classifications that only take into account the observable and measurable characteristics of the soil. But the distinction between the two types is less distinct than it appears at first sight. In fact, all classifications have behind them genetic preoccupations although they endeavour to propose to the user the most rigorous rules for identifying soils.
