Deleuze begins this series by examining causality dividing it into the causality of bodies in their depths (and the depths can go down to the quantum level), and the causality from the incorporeal effects that result - quasi-causality. Destiny results from both causes from bodies and quasi-causality. The former acts from necessity, but this shifts in quasi-causality to expression. Moving from necessity to expression suggests free will. "The Stoic paradox is to affirm destiny while denying necessity."
What are these expressive relations of events? Events appear to have relations of compatibility and incompatibility with one another. Chyrsippus looked at hypothetical propositions with conjunctions and disjunctions (eg. If it is light, it is day) and concluded they expressed their relation as a non-casual correspondence. "Astrology was perhaps the first important attempt to establish a theory of "alogical incompatibilities and non-causal correspondences. Deleuze examines identity and contradiction. Is that necessary for events? Moves to Leibniz and compossible and incompossible worlds. Moves away from Lebiniz because he excludes predicates of incompossible worlds from each other. Deleuze wants to affirm their difference have them communicate through each other through resonance. When their difference gets affirmed, but not conjoined, he calls this a disjunctive synthesis. Three kinds of synthesis: 1. connective synthesis ( "if ... ,then ...") which forms a single series. 2. conjunctive synthesis ("and) forming convergent series (worlds). 3 Disjunctive synthesis (either/or) which distributes the divergent series. Example of Nietzsche affirming the difference between his sickness and health by his gaining the know-how of reversing perspectives. Recommended reading: It helps a lot to read two of the books Deleuze cited in the previous Series - the chapter on Zeno (beginning of Book 7) from Lives of Eminent Philosophers by Diogenes Laertius and "Meditations" by Marcus Aurelius.Also, cited in this Series, De Fato by Cicero. You can read this here.
The paper, Cicero's "De Fato" in Deleuze's "Logic of Sense" by Michael James Bennett shows the basis of quasi-causality in Stoic thought. A pdf can be downloaded here.
For more on the disjunctive synthesis, Deleuze cites the third appendix in Logic of Sense called Klossowski or Bodies-Language.
