i am always a little puzzled about the five aggregates.
What is mental formulation? and don't these five aggregates
overlap somehow, like feeling, consciousness, perception,
sensation...
You see a lump of thing over the road. You don't know what the hell
is that. This is visual consciousness [pure visual
awareness/vinnana], or sensation [feeling tone of pleasant,
unpleasant, neutral/vedana]. Those are pre conceptual. You
recognise 'Oh my god that is Gold!' That recognition is the
begining of concepts. This is called perception (sanna). The sense
of self arise 'I saw it first! This is mine', obsessed with
craving, followed by the mental intention and plan to run towards
it and acquire it. This is mental formation (sankara), aka
Karma.
Commenting on karma, Buddha says 'What one intends, what one
arranges, and what one obsesses about: This is a support for the
stationing of consciousness. There being a support, there is a
landing [or: an establishing] of consciousness. When that
consciousness lands and grows, there is the production of renewed
becoming in the future. When there is the production of renewed
becoming in the future, there is future birth, aging & death,
sorrow, lamentation, pain, distress, & despair. Such is the
origination of this entire mass of suffering &
stress.'[11]