This article deals with adjectives which, in French, are used to estimate subjectively a quantity in sentences such as Ce salaire est bas, ridicule (Those wages are low), Ce livre est épais (This book is thick), Cette pente est faible, douce (This slope is smooth). Howether, these adjective do not all have a quantitative sense as such. We therefore try to define under what syntactical and lexical conditions they can have such a quantitative meaning. Among other characteristics, they are quite unique as far as gradation is concerned. Two kinds are easily identifiable, one with adjective that can only used with nouns expressing measure, the other with adjectives that can qualify concrete objects or human beings. The latter highlights both an approximate quantity and a sensory quality. The main point was to prove that such a subjective semantical phenomenon could be described in syntactical and lexical terms.