Status of commonsense knowledge in the mind.

Suppose someone introduces you to 2 boys and says - This is John and this is Jack. They are friends.

Now one relevant commonsense inference here is - They know each others' names - by using the commonsense knowledge that 'Friends know each others' names'. 

The fact that they know each others' names strikes us while we need it to use it to construct some thought. It doesn't strike us plainly and only and explicitly that "oh, so they must be knowing each others' names" when we are just told that John and Jack are friends. For example, suppose we want to ask one (say Jack) if he also studies with the other (and not just plays or hangs out), then, it will be processed, as a "check" in the mind, as a requisite thing, that they must be knowing each others' names, before we are about the say "So Jack, do you also study with John (or do you just play)?" (When you talk to Jack about John by uttering John's name, you are assuming that Jack knows John's name and thus, ONLY AT THAT TIME, the commonsense knowledge strikes you / gets processed in your head / becomes active, that friends know each others' names).

Commonsense knowledge comes to mind only when it is to be used. Otherwise it's "passive".