The Visuddhimagga (Path of Purification chapter XVIII, 25) explains:
For this has been said:
'As with the assembly of parts.
The word "chariot" is countenanced,
So, When the khandhas are present,
'A being' is said in common usage'
(Kindred Sayings I, 135)
... So in many hundred suttas there is only mentality-materiality which is
illustrated, not a being, not a person. Therefore, just as when the component
parts (of a chariot) such as axles,wheels,frame,poles... are arranged in a
certain way, there comes to be the mere conventional term 'chariot', yet in
the ultimate sense, when each part is examined, there is no chariot, ... so
too, when there are the five khandhas of clinging there comes to be the mere
conventional term `a being', `a person', yet in the ultimate sense, when each
component is examined, there is no being as a basis for the assumption 'I am'
or 'I'; in the ultimate sense there is only mentality-materiality. The vision of
one who sees in this way is called correct vision.