Research on the modal particles in Ancient Greek has mostly focused on speculations on their prehistory based on Homeric Greek or generalizing about their synchronic distributions (esp. in Classical Greek). Instead, this article details the diachronic spread of the modal particles in different modal constructions from Archaic to Classical Greek. It highlights those cases where its obligatory presence resulted in a different modal meaning (e.g. counterfactual and habitual usages) and critically discusses those cases of optional presence in Archaic and Classical Greek that prescriptivist grammarians have discouraged (e.g. with the future indicative and potential optative). Focusing on innovations allows us to (re)construct a chronology of the modal particles and their diachronic role in the Ancient Greek mood system, e.g. the replacement of the counterfactual optative by the indicative and its subsequent syntactic spread, and the creation of the past habitual and generic indicative replacing the habitual and generic optative (commonly dubbed 'iterative'). Finally, it is suggested that a similar diachronic approach which distinguishes between obligatory and optional presence could clarify the distribution of the modal particles in more complex areas such as Homeric Greek or the Ancient Greek dialects.