Trachomedusae (detail), Ernst Haeckel, Kunstformen der Natur. Chromolithograph 32 x 40 cm, Verlag des Bibliographischen Instituts, Leipzig 1899-1904. Photograph by D Dunlop. |

Events are often arranged in ordered-sets called **chains of events**. Then the subscript in an event's symbol is used to indicate location in the ordered-set. In general any sensation can be used to organize order. And to be put in order, events must be somewhat different from each other. But grouping events together in a chain also implies that they have some common characteristics, at least enough to establish membership in the set. We often use the letter P without a subscript to represent these common attributes. The chains themselves are usually refered to using the Greek letter psi

$\Psi ^{\sf{P}} = \left( \sf{P}_{1} , \sf{P}_{2} , \sf{P}_{3} \ \ldots \ \sf{P}_{\it{k}} \ \ldots \ \right)$

For a specific example, we can organize the events described earlier into an ordered-set where they are ranked by their thermal character; hot, to tepid, then freezing

$\Psi = \left( \sf{R}_{\it{a}} , \sf{R}_{\it{c}} , \sf{R}_{\it{b}} \right)$

And here is another example where events are arranged by their somatic attributes, left to right

$\Psi ^{\prime }= \left( \sf{R}_{\it{b}} , \sf{R}_{\it{a}} , \sf{R}_{\it{c}} \right)$

Please note that ordering events in these ways does not depend on any preconceived notions of space or time, events are ordered by their sensory qualities only. But later we will use $\Psi$ as a mathematical way of representing chronologically ordered experiences. Then as we go from discussing individual-events to chains-of-events our reports get animated. Chains may be called histories, processes or movies.

Summary |

Noun | Definition | |

Chain of Events | $\Psi \equiv\sf{\text{an ordered set of events. }}$ | 2-14 |