Via Steve Shaviro:

 

The word ‘decision’ does not here imply conscious judgment, though in some ‘decisions’ consciousness will be a factor. The word is used in its root sense of a ‘cutting off.’ The ontological principle declares that every decision is referable to one or more actual entities, because in separation from actual entities there is nothing, merely nonentity — ‘The rest is silence.’
—     Whitehead on decision: Process and Reality 43