This paper studies the language of the hypothesis and probabilities as used by the genevan naturalist and philosopher Charles Bonnet In his early works (1745-1754). Much concerned with experimentalism, he does not almost use this language, whereas he employs it in his works of maturity (1762-1783). The paper relates this emergence of a "doctrine of probability and hypothesis" to the Eighteenth Century shared language of scholars, as well as to the bonnetian project of grounding a logic for experimentation