An important thrust of Souriau's idea that ontology is centrally connected to the relation of bringing about (and not to that of finding out) is that what is brought about has consequences beyond those that strictly have to do with what brought them about. Consider tense perspectives. They bring about events, as a product of something that passes. Events are located in time, further they are located in tense: they are passing. It is what I call Generalized Doppler Effect. Just like in the common Doppler Effect that requires a still or a slower perceiver to hear the sound of a passing car, something needs to be held still or moving more slowly in order for the passing of the events to be noticed. In fact, it is only for what is still or slower that events happen – and therefore that something takes place. An event can only take place in contrast with surrounding states that remain the same (or change in a different pace). So we say that the river waters flow and we say that because the banks of the river stay put, it is only relative to the roughly fixed banks that the waters flow. It is the difference in speed, and ultimately the tense perspectives that give rise to passing events. Passing events are like the buzzing sound associated with the Doppler Effect: they can be heard only from a certain perspective. And yet, passing events, like passing cars, are as real as anything can be.
Image by Banksy