a condition that must be met for something to be in the class under discussion
a condition that needs to obtain in order for an event to take place (e
where p and q are statements, p is a necessary condition for q if q cannot be true unless p is true; it is impossible for q to be true and p to be false; if p is a necessary condition for q, then the conditional "ig q, then p" is true.
A condition that must be the case in order for something else to follow. Oxygen is a necessary condition for human respiration (though you may have plenty of oxygen around and still not be able to breathe, as when being throttled). Necessary conditions become the consequents of conditionals.