Full Idea
While necessity and possibility are interdefinable concepts, it is the idea of a possible world or situation which is intuitively primary.
Gist of Idea
The concept of possibility is prior to that of necessity
Source
Laurence Bonjour (In Defence of Pure Reason [1998], §1.3)
Book Reference
Bonjour,Laurence: 'In Defense of Pure Reason' [CUP 1998], p.12