How I remember it:
A is necessary for B:
The falsity of A guarantees the falsity of B.
A is sufficient for B:
The truth of A guarantees the truth of B.
A is necessary and sufficient for B:
B is logically equivalent to A.
A is neither necessary nor sufficient for B:
B cannot be determined from A.
RE: Steemit Critical Thinking Miniseries #5: Necessary & Sufficient Conditions [dTube]