The Western notation of rhythm is a writing of time. Its signs have a history. Everyone knows the principle of modern notation according to which "two quarter notes are worth one half note". This system, univocal and binary, is the result of the evolution of a notation which emerged in the thirteenth century, governed by the ternary, thought of as a trinitarian perfection, in which, although it is precise, there is no absolute relationship between the graphy of the signs, their name and their duration.
Over the next two centuries, the wide variety of invention and ingenuity of this writing of rhythm resulted in a proliferation of signs, often equivocal, and their rules of interaction. Better still, at the turn of the fourteenth and fifteenth centuries, as time was henceforth thought of as continuous, proportions were used. Since then, this richness has disappeared, but modern notation may still contain some vestiges of it.