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**These are excerpts and elaborations from my book "The Nature of Consciousness"**

During the 1980s several
techniques were proposed for re-founding Physics on a more practical basis. John McCarthy's “Situation Calculus” (“Situations, actions, and causal laws”, 1963)
represents temporally limited events as "situations" (snapshots of
the world at a given time), by associating a situation of the world (a set of
facts that are true) to each moment in time.
Actions and events are represented mathematically as mathematical
functions from states to states. An
interval of time is a sequence of situations, a "chronicle" of the
world. The history of the world is a
partially ordered sequence of states and actions. A state is expressed by means
of logical expressions that relate objects in that state. An action is
expressed by a function that relates each state to another state. The property
of states is permanence, the property of actions is change. Each situation is expressed by a formula of
first-order Predicate Logic. The
advantage of this logical apparatus is that causal relations between two
situations can be computed. The elementary unit of
measure for common sense is not the point, but the interval. Which interval
makes sense depends on the domain: history is satisfied with years (and
sometimes centuries), but birth dates require the day. Points require Physics'
differential equations, but intervals can be handled with a logic of time that
deals with their ordering relationship.
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